How much would a insurance agent make a year working through a firm like state farm or allstate in a small town of about 20000 people.

That would depend on a lot of things: If you were paid on business already in place, how much new business you could get, how much competition there is in the town, etc...

A slightly wild/slightly educated guess: about 25k per year, give or take 5k for the "depends on" issues.