I am currently building one. Aimed for £1000. It's looking like £1050 with all but stem and bars being new but on offer.
deore mechs £60 merlin
raceface ride xc crankset £65 merlin
cassette and chain 329 merlin
wheels £150 SSC
headset, stem, pedals headlock 2nd hand
fox float RL forks £300 (a steal) on one
As a total beginner, Im finding it much more fun learning than just plumping for the 1K boardman