4 grand for the engine swap don't sound too bad?
these people are professional and are hardly gonna do it for free? but they'll do a spot on job, it'll work when you get in it and they'll offer a degree of aftercare, which a breaker that sold you the 20v turbo for £1500 wont?!!?
consider pricing an engine, gearbox, wiring loom, ecu, drive shafts... etc etc..
i've put a 16v in my mk1 which is considered an easy conversion and to get it right it costs plenty!!