If you are a Passport America member:
http://www.passportamerica.com/cgdet...1644&zip=51521 at Avoca, IA. Regular price is $20-22. PA is $10-11
http://www.passportamerica.com/cgdet...1969&zip=50111 at Grimes, IA, a couple miles N of Des Moines. reg price 27.50. PA is 13.75
I haven't checked my TL directory to see how either is rated by them. I have no clue whether these are good or bad parks.
I can't get into the Escapees site right now to check that. If you need more options, post back and I'll dig out my Escapees and Trailer Life CG directories.