There is not much chance of you finding a 635 for 100$ or less. The lower power diode alone is 40$ plus 20$ for driver and what not, around another $40 for a host and heat-sink, there's your 100$ you still need batteries, a lens, and most builders like to make a little profit as well.
Blords build quality is top notch, I would definitely take him up on the 650 if I were you. I almost bought that last one and I already have an equal powered 650, it just looked so nice in the red 501b host. Plus you get an awesome run time with that lower powered diode and big heatsink in that host, you really cant beat it.
Good luck with your search either way!