Bottom Bracker (£39) :
http://www.ebay.co.uk/itm/151341769643?_trksid=p2055119.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT
Expensive NOS GA hubs (I was VERY lucky to find used ones for £20! but not in nice conditions, albeit they run smooth):
http://www.ebay.co.uk/itm/390745264869?_trksid=p2055119.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT (but as you mentioned it's gonna be a cheap build, you might get these: http://www.ebay.co.uk/itm/251441138538?_trksid=p2055119.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT)
Headset: http://www.ebay.co.uk/itm/Vintage-Shimano-105-Golden-Arrow-Headset-English-Tread-VGC-/151336298460?pt=UK_sportsleisure_cycling_bikeparts_SR&hash=item233c58a7dc
@anidel started
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Bottom Bracker (£39) :
http://www.ebay.co.uk/itm/151341769643?_trksid=p2055119.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT
Expensive NOS GA hubs (I was VERY lucky to find used ones for £20! but not in nice conditions, albeit they run smooth):
http://www.ebay.co.uk/itm/390745264869?_trksid=p2055119.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT
(but as you mentioned it's gonna be a cheap build, you might get these: http://www.ebay.co.uk/itm/251441138538?_trksid=p2055119.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT)
Headset:
http://www.ebay.co.uk/itm/Vintage-Shimano-105-Golden-Arrow-Headset-English-Tread-VGC-/151336298460?pt=UK_sportsleisure_cycling_bikeparts_SR&hash=item233c58a7dc