If you are staying off site at either the Days Suites or Days Inn right next to Old town, they'll give you free ride coupons. If not, get the coupon book at the guest services center in Old Town. It has a lot of buy one get on ride free coupons. Along with coupons for totally free rides on the ferris wheel.
It is a nice way to spend an evening. I have to second Flippers pizza (in Old Town). Pretty reasonable in price and excellent. We get it several times each trip. If you are really trying to stick to a budget though and your kids will really want to ride the rides and play the games, it may not be the right way to go. There isn't a whole lot else to keep young ones interested. (if you're taking kids that is).