Sleepy Hollow RV Park is within walking distance to Los Algadones. I know it's on the CA side, but if you want to walk back to your coach and sleep, it's the best place to stay. Especially if you will be under some type of meds.
For price, there are so many RV campsites from dry camping to full range hookups. In May, you might be able to ask for a discount as they will not be full. I like the foothills by Fortuna Rd. There is a large grocery store called Fry's that is wonderful, and Walmart is close by as well. Some that are in this area are Blue Sky (by the freeway), Western Sands, Adobe Village, Sunset Palms.
I'd also recommend for Yuma travelers, Hidden Shores RV Park. We have been enjoying that place for years. They have spots right on the Colorado River, and it's beautiful and well kept year round activity. They have a nice beach right by the RV spots that you can enjoy the river. They have clean showers, laundry facilities, gated security, a playground, restaurant, general store, a little golf course, pool area, boat docks, offroad trails, horse facilities, etc. Plus, they are cheapers than a lot of KOAs that we've stayed at. They do have a rule on RVs though, if it is more than 10 years old, it will need to be approved by management.