The research I did tells me the XCR might be somewhat comparable to the Rockshox XC30 but I read a message from someone saying he broke two Suntour XCR forks twice in 13 months. I just bought a Rockshox XC30 but I can't review them as I haven't tried them yet. (Will likely buy wheels this summer to complete that project.) Maintenance parts are also available on eBay for the Rockshox XC30.

Cheapest price I found for the Rockshox XC30 in black was from hibike.de. I haven't tried that site so I don't know their reputation. Mine were ordered from Acycles.fr but mainly because I wanted them in white.

The Suntour XCM isn't really recommended from what I've seen.

(You can also notice whether the forks you're looking at are for a tapered fork or straight, 9mm QR wheels, travel etc.)

EDIT: Oops, I forgot you're looking for 650b. The prices I was talking about were for 26 inch.

Here's a Solo Air XC30 on sale for $170: http://www.blueskycycling.com/produc...5-9mm-Fork.htm
(That's 120mm travel though, some frames only take 80 to 100mm travel.)

ANOTHER EDIT: You may be able to use 26 inch wheel forks for a 650b wheel. There might be a way to modify the one I linked up there to 100mm or 80mm but you'd have to check.