You can spend a little or you can spend a lot. However there are several things to consider before spending too much. These days age doesn't necessarily make an item worth thousands of dollars. Some pieces are obviously worth every penny from hand carved decoys to fancifully painted whirligigs.
Folk art comes in many guises.
When it is 20th century it can be stone carving, chain saw carvings of wood, a simple painted plywood form such as the cars done by Howard Finster, or carved and painted walking sticks and canes. I am reminded of the tale of the Emperor's New Clothes. To refresh your memory, the Emperor was sold a bill of goods in the form of an invisible robe. When he paraded it before his subjects they applauded and praised its' elegance. It seems that today, folk art aficionados and gallery owners seem to heap praise on anything that can be termed folk art.