ahhh yes..... the lureee of the luminorrrrrr

yeah just go through the dealer section, since you are in the UK, i'd say try buying from Narikka, since he is in EU as well he can source the watches you want.
if you truly want extremely cheap pams... then PWC is having these crazy daily specials... with $50 111h!! but he ships from asia... so there's some chance of customs risk.
seamaster... planet ocean? then the 45mm has the UPO (ultimate planet ocean) which is the best.. and you can mod the hell outta it.
if you are looking at the 42mm PO, then that can be modded to the max also... just use the search function and look @ Pugwash's tutorial.

good luck