I have had a 55 gallon FW tank for years and all I ever use is rubber lipped plecos they grow quite slowly and don't get very big max size at best 6". I have only had one in the tank for the last 6 months and not a spot of algae on the glass and it is only approx 2.5". Plus they have them at petsmart for usually around $6 so they're in your budget too.