Can you pm or tell where you found all the parts? I'm seeing around $2,000...
I bought mine off HKPRO as a USC with all the parts. I was planning on just getting a USC then buying all the parts separately, but I found the whole package for the price of a new USC.
They make a lower that uses grease gun mags, and that can be cheaper in the long run. The ump mags are really expensive if you can find them.