We have stayed many times at Terribles Lakeside Casino in Osceola, IA. The price is right at $20/night (no credit cards) and with a Players Club Card, you get $10 back in free play. One piece of advice is to get your player's card BEFORE you pay for your camping. All sites have full hookups and there is NO limit on length of stay. All campers are entitled to the amenities of the hotel, including pool and use of computer in hotel lobby area (no wi-fi).
Friday and Saturday nights there is a seafood buffet featuring crab legs and they are delicious. Price is very reasonable.
Not sure of the exact number of sites but there are plenty. They start filling up around 5pm or so, especially on weekends. There is also a free shuttle that will pick you up in campground and take you to casino. Casino is also within walking distance. Plenty of slots on 2 levels. On lower level there is a non-smoking area. A very nice place to stop for a few days and relax, eat and have a little fun. Very convenient right off I-35.