Lum's was a chain restaurant that had a location on the corner of 7th and Liberty. It opened in the middle 1970s. Not sure when it closed. It was one of those sit-down places with a wait staff that was an alternative to fast food, but still with fairly modest prices.
The house specialty was a hamburger called the "Ollieburger," named after the chain's founder. The key to the Ollieburger was the secret sauce. On the way to looking up something else, I stumbled across the recipe for the Ollieburger. It's available here:
http://www.cyber-kitchen.com/ubbs/archive/SANDWICHES/Beef_Lums_Ollieburger.html
for anyone who might want to create the Lum's experience. It appears the whole chain has gone out of business.
Downtown used to have a bunch of those "middle" places which were a step above the fast food locations with plastic trays, but a notch or two below the spots that gave you concern about the cost. Some of the others I remember along those lines were Palmer's, Stouffer's and Sweet William.