brotherhood_of_LAN - 12:54 am on Mar 13, 2011 (gmt 0)
whatever suits you best
That's it, though a very generous offer all the same.
Consider how a cut to your traffic sources (google penalty or re-ranking for instance) would affect you if you owned the site, this makes a 10x earnings offer seem more generous considering it can happen at any time. Traffic from them is very easy to get used to.
Saying that, not many sites will get as much type-in traffic as you do.
Perhaps also consider if the niche has the same earning potential in 10 years?