You can get a reasonably high spec core duo pc for very little if you DIY it, or get it built. (Assembly costs for a whole pc in Switzerland is about $100)

To look out for primarily is a power supply above 460w (music pc's get all sorts of stuff plugged into them), a solid harddrive that runs at 7200 rpm (ideally 2, or otherwise a big one you can partition - c: for system, d: for audio), 2gb of ram (top of the old line ddr2-1066 like the kingston hyperX pc2-8500 is relatively cheap now), and optimized for XP pro as Vista is apparently still too crap. Also make sure the Firewire plugs on the mobo, or the Pci card you install has a Texas Instrument chip. Loads of issues with others even though VIA seems ok as well.

Good HD's:

WD Caviar (blue), Seagate Barracuda

Good Ram:

Crucial, Corsair, Kingston, OCZ

Good motherboards:

Asus, GigaByte, Intel


Can give you specs for an awesome pc that will use some older parts (2006 release) to cut costs. Let me know!