Best place to farm money in Borderlands 2
Solution 1:
Go to the fridge and farm the crystalisk, it's pretty good for money.
Solution 2:
Really good way to farm money is during the Mission to save Roland. Just complete that mission over several times and you can build up a fortune of around 100,000+.
Another good way to farm is to use the Slot Machines in Sanctuary, but the trick to it is, make sure you have a full party. For each time you win money on the slot machine, everyone else in your party does as well. Just cycle out between 2 people and keep gambling and selling any weapon that you aren't interested in.
My party made around 50,000 in about 2 hours, not too mention, we got some pretty fantastic weapons.