Eventually you'll deplete some merchants of their gold, even without farming (at least Grimm and Sassan, since they are relatively easy to get to and don't start off with a huge amount of gold).
I just started on Stone's fortress, and the first section you can do was relatively easy (with opponents in groups of 1 or 2). However, the difficulty jumped a fair bit flying up to the next higher section (at least in part due to me being out of practice dodging, since most of the last dozen character levels were so easy).
