Tournaments, and trade. Killing bandits is way too slow to make cash.
As for trade, go doing some little search by yourself on this forum, there is some very interessting information about trade written by myself and some other fellow traders.
Beware with trade: once you will start trading in this game, you gonna be addicted to it since it is the most reliable source of cash, leaving you with no room for those nearly worthless loots, so better have good inventory management skill
ie: with the iron trade, i can make with only 5 iron bar (so 5 slots) the same amount i would make by reselling my full inventory of bandit loots, on days they have decent stuff on them...