The reason for the high charge is:
a) It costs me personally about $100/mo to lease the server. If that were split 4 ways, it would be $25 a person. Unfortunately, the only people who have taken up the offer so far have been loial and superman (for a while), so I'm still paying most of it.
b) I don't want too many servers running on the machine or they will degrade the performance. If I charged less, I'd need to have more people involved to make up the difference.
c) It's a pain in the butt dealing with people when money is involved. I'd almost rather pay for the whole server myself than deal with getting people to send me payments. Charging a higher amount keeps the less serious (and more troublesome) people away.
You aren't required to get a server from me, of course. If you find a better deal elsewhere, go for it -- it's probably better to have servers running at different locations anyway.