A local technician can easily replace a worn-out potentiometer if Creeper's cleaning suggestion doesn't work. Personally, I've never had any luck rehabbing pots with tuner cleaner - all the ones I've tried this with were physically worn out as opposed to simply corroded or dirty. It's well worth a shot though.
B&K also has made power amps with output controls that may fall into your pricerange or a little above - also check out Parasound as you've mentioned.
In most cases however, the volume controls on a power amp are going to be up back by the amp's inputs and outputs - that may present a usability problem. I'd also guess that these typically smaller volume controls are not going to be as robust as a volume control designed for more frequent use - they may wear out rather quickly with regular use.
B&K also has made power amps with output controls that may fall into your pricerange or a little above - also check out Parasound as you've mentioned.
In most cases however, the volume controls on a power amp are going to be up back by the amp's inputs and outputs - that may present a usability problem. I'd also guess that these typically smaller volume controls are not going to be as robust as a volume control designed for more frequent use - they may wear out rather quickly with regular use.