How do I make a lot of money efficiently?

Far Cry 3 has a relatively expensive item economy, IMO, and money is a little hard to come by when you're at the early parts of the game. Compared to some of the other games I play, I find myself having to frequently grind killing people, and manually collecting the loot of every fallen individual just to get a little money.

What are efficient ways to get the big bucks (maximum money for minimum effort, preferably methods which are repeatable) in Far Cry 3?

EDIT: I'd like to add that at later parts of the game, money is no longer an issue. My problem now is where to spend it. Even though my wallet has reached the maximum crafted capacity, I'm still hitting the limit. =)

I have the opposite problem, I have too much money, so I must be doing things differently than you...

Here's what you should do to earn money (or save on spending):

1. Don't buy weapons. As you unlock radio towers, weapons will unlock for free at vendors. Picking weapons you didn't buy/unlock off enemies seem to unlock it for free as well. There are a few "Signature Weapons" which are unlocked after certain milestone (e.g. Finishing enough missions, conquering outposts), these are expensive, powerful versions of other weapons with pre-installed mods and paint jobs, needless to say, they cost more than just the mods alone, sometimes they are worth it.
2. Don't buy medicine. Make health syringes.
3. Don't buy body armor. Waste of money IMHO.
4. Sell off loot. When you loot bodies/chests, you usually get an item as well as some cash. Visit vendors often and sell this stuff.
5. Upgrade your loot capacity. This will extend the times between you "selling visits".
6. Upgrade your wallet. You don't want to end up losing money because you looted a chest or finished a mission when it was full.
7. Spend your money on maps, but only if you're the exploring type. These show you loot chests locations on the map, they cost quite a bit but should return investment if you go out of you way to loot chests.
8. Do the side challenges. The stars on you map represent score challenges that are free to try and net an XP bonus as well as cash when you reach a certain score. There are other challenges like racing and gambling which require you to pay in order to play but only reward if you succeed. Save before them and reload if you lost money.
9. Sell off excess skins. Check out crafting guides online. See if you need the skins you have in your inventory, if not, sell. Check for animals in your area with good skin values and hunt them for their skins. Tigers have the highest skin value, but I found Cassowaries, while having average skin value, are easier to hunt and come in large packs. Sharks aren't too hard to hunt as well when they're close to the beach.
10. There are a few skills which help with money, they're unlocked late in the game, though. Dealmaker which gives you 25% more cash when selling loot; Penny Pincher which makes more money appear on looted bodies; and Loot Takedown which automatically loots bodies when you do a takedown (close range takedowns work, not sure if it works with knife/gunslinger/grenade takedowns).
11. Use ammo caches and pickups instead of buying ammo. While refilling your whole ammo at vendors gives a certain discount, many missions in the game and several enemy outposts have ammo caches available in them. Unless you're really running short on ammo, you can safely start missions without buying ammo beforehand. After taking over enemy outposts, check for ammo caches, usually near the door leading to the fast travel/vendor location. These may disappear after the location has turned friendly and you revisit it.

To add to this answer (also, these are more important in the earlier-middle parts of the game as in later parts of the game, money will no longer be an issue):

• The 'Refill Inventory' option when buying in a shop refills the ammo for all equipped weapons, throwables, and explosives for a 20% discount. Buy those items through this option whenever possible.

• To make it easier to sell items whose 'Recommended Use' is 'Sell', use the 'Quick Sell' option when selling. This will automatically sell all 'Recommended Use: Sell' items. This will save you time and avoid you having to manually sell each of those items.

• 'Quick Sell' doesn't automatically sell animal skin, so you'd have to manually sell each piece of the animal skin you get. Since it also takes some time to hunt, find the carcass and skin animals, I won't recommend you do this if you want to gain money fast (especially in the early parts of the game where you don't have access to powerful weapons to kill animals with).

• Bring a repair tool with you. A common random event will have a Rakyat warrior or a civilian have a car that needs fixing in the side of the road. Fixing it for them with the repair tool will net you $50.

• Looting each dead enemy take time as you'd have to have to find the corpse of each fallen enemy (which is not easy in most situations) and wait for the 'search' animation to finish for each. To save time:

  • In the 'WANTED: Dead' quests, make sure you at least loot the person you have to assassinate by knife. He usually (or possibly, always) carries an expensive item.
  • The 'Loot Takedown' skill will allow you to automatically loot enemies you killed by melee knife takedown. Use with the 'Chained Takedown' skill for more fun (and faster loot collection).
    
    

• Repeating the Don't Buy Weapons! advice (except for signature weapons). This is probably the most important advice, especially in the earlier parts of the game, as weapons are expensive. Just activate as many radio towers as possible to get weapons for free. You'd usually want to save your money to buy weapon attachments, signature weapons (which are expensive but very powerful and allows more attachments, compared to their non-signature counterparts), and maps (which will show the location of loot and collectibles, leading to more money [and XP]).

Poker, plain and simple. Save before you play. Go all in with at least one face card, especially if you think it will be high card, others will usually fold and those that don't you'll usually beat and take all their chips quickly. If you bust reload and do it again. each game nets you 1k so you can fill your wallet in no time. By far, the most efficient way to get money.

Follow the other's tips on not wasting money, they are right on the ball, but not so much their methods of making money. You should honestly just ignore them because they are eventually a waste of time. Just stick to poker to make money, Only collect pelts/skins when you need them to upgrade equipment. You should really only try to keep plants for recipies in your inventory at all times so you can make what you need when you need it. Any other junk items or skins are just a waste of space.

Easy get a boat and run over sharks. Get the perk that gives you two skins per animal and you will get 60$ per shark. I got tons this way near the starting village. It works, trust me.

Poker is an extremely great way, but if you feel like you are "Cheating" then play the jet ski racing game near the exit of amanaki village near the river. $120 every minute and ten seconds. Really good money.