I have looked at these a few times and come over all misty eyed. I want one so bad but the cost, the weight, where to put it, what to do with it are questions that, cannot, sanely. be answered. Would one be enough? you would have to have at least 2 so now up to 10,00 quid.
There are a few companies making after-market parts, such as Armorpax in the UK and 6th Scale Icons. (Interestingly the guy that runs 6th Scale Icons in Las Vegas - Mike Stannard - is an ex-squaddie - Pompadours I think).
If you want something cheaper and lighter Dragon Models have released 1/6th scale plastic Pz.Kpfw II as a built piece and a kit, and the Sherman as a built piece.