How mechanicaly apt are you? I've seen the fan assembly on ebay for about $10 and I've torn my 8100 down a couple of times. It isn't very hard, but you do need to pay attention to some of the details. Having it done will easily cost you $100 or more.
If you want to get an idea of what you're in for, here
is a link to an illustrated guide on how to get at the cpu and fan assembly. If you have any problems withthe link, PM me your email and I can send it to you.