Well, heck - while all of the crypto mining devs are having fun offering toys for sale, how about:
2 BTC for a 15-20% speed boosted version (on my very large test machine, goes from 312 hash/s to 380 hash/sec). x86 specific.
Exclusive; it goes to only one person. You get any speedups I make in the next day or so while I keep poking at it, though I don't guarantee results past what I've already got running.

PM me first, since I'll only sell this to one person.
(Of course, that "one person" can also be "please open source the changes" - or "I will resell it", or "I will share it with my friends". I'm agnostic. I'd love it if you asked me to open source it, really.)