What are your size restrictions for the center channel?
Infinity makes an in wall center speaker for 159$: The ERS HV250
Also, matching in-walls: 4 of the Infinity CS60's for $90 each. http://www.crutchfield.com/p_108CS60...60.html?tp=192
For a sub.. Many 10" subs are available that might suit you such as the Infinity PS210 for 299$