I am putting this here as once in a while, these lists change
https://blog.cheapism.com/best-cheap-burgers-in-america-15292/#image=1I have been to the ones listed in Minn. and Indiana .
The place in Madison , Ind. is definitely worth a visit, their chocolate shakes are fantastic but have gone up in price a bit.
Matt's in Minneapolis is way below any competition and they are good old fashioned burger joint burgers.
Cheap burgers in Detroit their pick is bs, Telway, on Michigan St. (U.S. 12) you could get five burgers the price one at the place listed or Elmer's on W. Chicago where you could three for the price of the place listed ARE cheap burgers in Detroit.
Nick's Burger Shop in Brookings, SD is the cheapest I know of at $2.19 for a plain burger.