if he's a masher then yeah it might make sense that he need taller gears. Some people just do better mashing...i don't see any sense in trying to stop 'em doing it if their knees can take it.
**EDIT** I'm a 'tard, you need a freewheel...i linked to freehub Cassettes.
might wanna look for a 54T chainring too.
**edit**
here's one, but like you said...not cheap. $45
http://www.amazon.com/Sugino-54t-110...1&sr=1-1-fkmr2