I don't know for sure what the contract is, but a standard server from our ISP with 2x quad core, 2GB of ram, and some bandwidth a month is $500, for just ONE server. Our leased server is a lot more than that, plus we have 2 servers. Just for the servers themselves I would imagine it's around $1000/month and I am certain we go over our bandwidth allocation by a lot which then is another additional cost. The 3rd server which I provide, a server I own and shipped to our ISP to host, costs me $109/month, which because we don't get sufficient donations I do not get any re-imbursement, and many many times we've gone over my bandwidth allocation, which is an extra charge. The most I, personally, had to spend a month for my server is around $220. My server alone only being $109 a month would need just under 8x people to platinum donate to cover.
The bulk of the cost comes in with the bandwidth though, which can vary from month to month, depending on how big of patches we make, how many people do Re-Patch all and re-download all the patch files, browse the forums, hit the website, etc.
We've been using my second zone server, to help keep the game running lag free, for almost a year now and I've spent over $1700.
It's not cheap. I'm sure most of you never realized how much time, energy, and money the GM's actually put forth to try an provide an excellent game for this community.