It depends which version you're after. I think there have been three versions of this model so far. The most expensive being the UCS (Ultimate Collectors Series) Lego 10227. This set is now retired and commanding around £250 for new in sealed box or £170 for used, complete with box.
There is also Lego 75050 which you can find discounted as cheap as £25 (rare at that price) when on offer But expect to pay £40+ for a brand new one.
Personally, I would advise the UCS. If you're going to build it, buy used but complete.