I had a similar dilemma a few weeks back and ended up getting a complete 2011 bike in a sale. It all depends on how much cash you want to drop on a frame/forks/wheels, obviously an On-One frame is perhaps the best budget option. Personally I demo’d and really liked the Pace RC129, but my budget just couldn’t stretch to one in the end (looking at about £1850 in the build I wanted).
I ended up getting a 2011 Giant XTC29er for just about £1250, and I’m over the moon with it – not just a good 29er, but an extremely good bike full stop.
p.s. oh, FWIW, I can really recommend the Hope hubs/Crest 29er wheelset – replaced the OE wheels on my XTC with ’em and they’ve noticeably perked up the bikes acceleration and handling.