100 x 29ers?
Well - here's your basic tubeset - http://www.cycle-frames.com/bicycle-frame-tubing/29er-Tubeset-38-X-858-DT.html - they're $78 a time
Bottom bracket - http://www.cycle-frames.com/bicycle-frame-tubing/LUGLESS-STD-69MM.html - $4.25
Dropout - http://www.cycle-frames.com/bicycle-frame-tubing/DO-W-DISK-BRAKE-and-DERAILEUR-MOUNT.html - $17.50
So that's $100 in hardware per frame, plus vat and duty and carriage, so thats about £85 landed for the bare frame parts.
Mitring everything up? Batch building? Save 16 joints per frame, 3mins per joint, that's 48mins a frame, say 75hrs, or 2 weeks per 100, say.
Then you've got to weld everything up - well... double the joint times? So let's say 4 weeks for that. That'd be about 4 frames a day.
Braze ons. Forgot them. Couple of bottle bosses, cable guides (5), 5mins a time? 35mins a frame - That's another 50hrs I guess- a week and a half?
Face the BBs and disc mounts? Another fifteen minutes a frame - 25hrs - call it a week?
So we're on 8 weeks labour, for a skilled worker - what? £6k, say?, spread across 100 frames is about £60 a frame?
Then you'll need to paint - £25 a time?
You'll need some boxes - £3 a box I'd have thought.
Decals - Fiver a time.
So we're looking at about £180? For something built in quite basic tubing.
You'd have to sell for double that at lest unless you were silly.
Plus the vat.
And you haven't costed in a jig (buy one for about £2500 or make your own).