My son is getting a '91 RS and it has the original speakers as far as I know with a Kenwood HU. He wants to add a box w/ subwoofers and an amp. Any suggestions that won't cost an arm and a leg?

I'm sure there are a ton of young guys on the board with limited budgets and have worked the process.

 

You must figure out how much. A popular choice that is fairly priced is a set of 12' Subs. Start with that, find an amp, then a radio unit. E Bay works great

 

I would start with a decent headunit and some speakers and then worry about subs. Loud bass with crappy vocals/mids is no good