J.S.
We go to the Dollinger family farm in Channahan -- http://www.dollingerfarms.com/pumpkins.htm
It's the old fashioned kind that doesn't have a charge for you to be there, but they charge for the train, corn maze and for any pumpkins or whatever you buy. They have play houses, slides, bunnies to touch, haybales to climb on -- all those things are free. So, you could go for free. I would take the kids on the train, though (assuming they like trains). I think it was $2/person last year, but it might have been $3.
There is also Seigel's cottonwood farm on Weber road near Caton Farm Rd. They have an entrance fee of like $6/person but there are coupons on their website for a couple dollars off. They have a bunch of jumpy things and playground areas, a haunted house. Seigels has more stuff and would be better for older kids. I prefer Dollinger but my kids are pre-school age.