My mother is an ace at getting cheap rooms. We would take a lot of family vacations growing up and I remember her calling around and saying all kinds of crazy things to motels. A few tips I picked up over the years are:
1) Make reservations early - as far in advance as possible. Many chains adjust there prices daily to reflect the changing business (similar to airlines)
2) Seek out coupons and deals in tourist literature
3) When you are on the phone ask for all sorts of discounts. You'd be surprised at what can be picked up. If anybody in your party works for the government ask for a military discount, If you are a triple A member, ask about that, keep trying things. Some large companies have corporate discounts. Sometimes just asking if they have any specials can turn up deals. I was once quoted a price and then I asked for a special and was told "Oh, yeah we do have some cheaper rooms available" Saved $20. I've gotten rooms in the Sandusky area for $40 during July, $50-$65 is my usual.
4) It is amazing how fast prices drop when you get a little bit away from Sandusky. I've often stayed in Milan near the I80 interchange and got a room pretty cheap. Still, there is the price to pay in have a further drive to the park but it never really bothered me too much.