The best bang for buck I ever saw for in-wall speakers was when the local Fry's Electronics was clearing out the Polk rc60 in-ceiling speakers for $49 a pair a couple of years ago. I bought two pairs and installed them in the ceilings of two bedrooms. Far from fantastic sound, but more than adequate for background music. I'd also consider them for rear effects speakers in a 5.1 or 7.1 system, but not for the front. I've seen them advertised recently, but the price has gone up to $99/pair.
-Rob