Valley Speedway in Grain Valley, Mo also has a midget class that they run on a regular basis for the past couple of years. It is even a sanctioned part of POWRi. The rules that I could find online look way lax. It is branded "Valley Outlaw" I believe that they have a bunch of different motor combinations in this group. They do not pay as much as you are suggesting. The car count is usually in the low teen range. Sometimes they have more sometimes they have less.
My love for midgets will take me to Valley almost everytime they run.