Wow. $4K (plus $30 shipping. I love that. Am I the only one that thinks they might throw in the $30 shipping?)
Then it's still a pistol, and you have to source the parts to make it an SBR.
Then you have to source the 922r parts to make it legal.
And the mags are $75 each.
And, of course, the $200 stamp.
That's a fair bit for an SBR.