How much then would this Window 2x4 core machine cost (roughly)

As I mentioned (i think) somewhere else on in this thread, I work in an office with a network of about 5 or 6 semi reasonable PC's ( from Pentium 4's with a gig of ram down to celerons with 256 ram for basic office work )
Together they made pretty much no difference when we hooked them up with rendercows - the first couple of runs we did didn't work very well at all
We then went on to use ONLY the Mac G5 we have

All we are trying to get ( on the strictest budget ) is a much faster solution
The Macpro looked good, and quite a lot faster
If at some stage we have the resources to add another fast machine - or somehow expand the Macpro then all the better.

Why doesn't some PC company out there make a superfast 'renderbox', specifically designed for 3D rendering for amatuers and semi professionals - with no other features but render power?  Maybe this is naive...