The terms are rather unfair to me (e.g. if the fork happens just before the deadline, then it's impossible for the minority chain to mine 2100 blocks) but I'll overlook that. As long as I also win if BU makes a failure of its fork (i.e. after some time miners realize the BTC chain is worth more, with lower difficulty -- so they switch back). In that circumstance by the end of the year BTC will be the fork with the most proof-of-work, even though at one time it was a minority.
Anyway, I'm happy with 1 BTC and will go as high as 100 BTC. May I suggest Dooglus as an escrow, but I'll take anyone of the standard escrows here.