£800 is pretty steep, especially seeing as it's probably just a g&g- which are less than £320 new.
The accessories could be bought seperatley and probably still come to less that £480. For £800 you can get a brand new TM 416 and a full set of mags and probably batteries too.
Yeah but the deal is for the gun, the accessories AND the paint job. Yes, it's a £320 G&G and yes you could get all the bits separately but then you'd have to paint it all up which while not massively hard to do is a relatively complex task that is probably beyond most airsoft buyers...(speaking as a custom painter with a vested interest of course )
If you went down the TM route then yes you could get the gun (£535 from Fire Support) and a bunch of mags (£22 each again from Fire Support) but you wouldn't get the extra bits..