Did you use the words (good and inexpensive) in the same sentence?
It sounds like your interested in wall treatments ---- you may consider building your own sound traps, this is the method I have used in every music room and studio I have ever treated -- DIY
In addition, There are also some silent recording options that are relatively in expensive, but you will need a preamp and headphone amplifier to make good use of these Items...
I have a Palmer PDI-03 for sale on the bulletin board right now, but their primary market is aimed at going direct into PA or silent recording...
The is a company that makes a small isolation cabinet called AxeTrak. I have seen them on eBay pretty cheap, but it's for recording also.
I personally don't care for the tone of ppimv mods or attenuators, may as well be using a pod imop...
This is the vid that sold me on the mass.. by the time you hear anything missing it's ridiculously quiet in the room and it's really just some sustain that's not there cause you need volume for feedback.