Kinesis FF29 custom built? I did a fairly decent build with change from £1,500 for racing. Weighs in at 10.4kg with basic Rebas and mid range kit.
Sensible price for the frame (especially for me as I got a mint one from ebay) and although it’s not a silly light frame, you can save the money for lightish bits. I’m running Hope Hoops with Crests which I took from my CX bike. No silly bits but as it’s 1×10 rather than 2×10, it still came in lighter than my old Kinesis XCPro3.
I think the On-One / Planet X 29er race thing was shortlived because of quality issues? Scandal 29er is often silly cheap if you want to dip your toe in the water though.