How to effectively level up a craft-based character?

If your speech skill is low, you can get your own resources by mining (good places to mine), hunting, chopping wood, gathering flowers, et cetera; although leveling up your speechcraft will make buying resources and selling products profitable, and it's fairly easy to do.

Buying cheaper alchemy ingredients can also be a good way to turn a profit.

Alchemy is the most profitable crafting type.

If you can manage to gather about 500 gold buy out all of the local alchemist of their ingredients, except for expensive stuff like fire salts. Then just mash ingredients together to discover properties and sample ingredients. Some great combinations of cheap ingredients can make expensive potions. Put together chaurus eggs and Luna moth wings to make invisibility potions. Deathbell and River Betty can make an expensive slow poison. Add random ingredients to your 2 ingredient potions to discover more properties.

Walking around the countryside can help you find lots of ingredients, so remember to harvest any ingredients you see when you are walking around. Swimming in rivers can help you find fish.

To get good prices from shopkeepers, items like masque of calculus vile and the thieves guild hood can get you better prices.

Once you get the hang of making expensive potions travel to all the holds and sell your potions to all the different alchemists, if the alchemist runs out of money, either go to another, or wait 48 hours and they will restock their money and ingredients.

If you manage to get to 50 speech skill, there is a perk that will allow you to sell anything to any merchant, carry around your expensive potions and sell them to any merchant you come by to make lots of money.

Start by creating 4 items (bracers, helmet, necklace, ring) that can be enchanted with "fortify alchemy". Go and create two or three "fortify enchanting" potions. Use the potion at the enchanting table and put "fortify alchemy" on the 4 items. Put on the 4 items. Then go back to the alchemy table and re-make the enchanting potion. The potion should be more powerful now. Repeat the process until you are at high levels of percentages (22-25%) on the enchanted items. Once the items are high enough, create potions like fortify health, invisibility, etc... Basically anything with wheat and a Giant's toe.

The only cost is a few leather strips and iron ingots for the equipment (silver ingots for the necklace/ring), and soul gems (which can be farmed in Blackreach or dwemer dungeons), and the wheat (which is rather abundant) and giant's toes are on giants (naturally). It takes time, but it is really not very expensive.