At that size of colo (5 boxes), you'd be in the same price range getting five dedicated servers; you may end-up with faster servers (rack-mount instead of desktop) and no hardware maintenance responsibilities.
I looked at it a year ago, and it looked like Dedicated was cheaper than colo, up to about 8 servers or so. If you have to budget staff time or compensation to have someone available to go fix the servers 24x7, then it takes a couple of racks of servers before break-even. If you don't need things fixed outside business hours, then colo becomes cheaper sooner.
I wouldn't colo a desktop, its a waste of space and power, they are not setup to be a server, I would suggest you switch to rackmounts and save yourself some money on space and spend it on bandwidth, a typical 1/3 cabinet can cost anywhere from $500 to $1000 including some bandwidth, but it all depends on your location, but if you don't care where they are located you can just shop around for best price.
Try and find a bread rack hosting provider. They can range from $50/mo to $150/mo depending on power/bandwidth requirements. Although rackmount is preferable when it comes to hosting, you can still do this with a bread rack if needed.
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