If you buy the components individually it would probably be cheaper. If you mean building the rifle from scratch, I'd advise against it. Why bother looking at that thing anyway? It'll be so much more expensive to make than any entry level AEG.
All the parts are (or at least were) available from PAS so it's pretty easy to price up. The gun itself is stock so you're paying someone £800 to bolt some bits on and spray it. Not worth it IMO.
If you mean building the rifle from scratch, I'd advise against it.
Why bother looking at that thing anyway? It'll be so much more expensive to make than any entry level AEG.