Dell is probably a good choice. My friend just bought one for around $995, or so with free shipping. Sometimes they offer Free Shipping, so look for the specials. I definitely do not like Compaq, as they can be hard to work on and suffer from compatablility issues. We just bought some IBM Net Vistas at work, with 17 inch monitors, but probably paid just a little more than that. It is hard to get a good deal on just 4 computers, but ask for it anyway. Sales should be a little slow right now.
What pushes the price up for a computer is a gaming or Multimedia intense Video card and DVD. So buying a computer with integrated video might work great for business computers. Probably want to get NIC cards for them all.
There are probably some good deals on some 1.2 Gig Celeron systems being moved in a clearance sell. I built one at home with a 1.2 gig boxed processor and an Asus TUSL2-C motherboard and a VisionTek Geforce 2 GTS-V video card. It runs great. This would be ideal for Business. A local custom computer shop could probably build them pretty cheap. If you do not like my post feel free to point out your opinion or my errors.