I co-locate my 4 servers. 3 I recently purchased for $835 each (1U rackmount, 2.4ghz p4, 1gb ram, 2x 40gb w/hardware raid1, dual 1000mb nics) my 4th server I purchased a while back off ebay for $500 (2U dual P3 550, 1gb ram, 2x 36gb SCSI drives w/soft raid1) The 2U is soon to be upgraded to a Dual P3 700mhz, and used mainly for backups and a game server.
My Co-location fees are: $250/mo for 1/4 rack (10U), and I purchase bandwidth for roughly $100/mo/128kbps(averaged), but it is fully burstable to 100mbs. It equates out to about $100/40gb transfer per month. I am currently paying for a 512kbps connection (averaged) which gets me roughly 160gb transfer per month, and I get a discount the more bandwidth I purchase. If I go over my average, it is $0.79/kbps extra which equals about $1.50/gb extra per month.
The bandwidth price is a little high, but I am fully burstable to 100mbps, and am sitting on 3 OC12's, which is what I care about. That and I have 24/7 physical access to my box for those 3am kernel recompile cravings