Couple suggestions that can be fun:
a) If you order directly from Bushmaster, you can skip out on the excise tax on complete firearms (around $100) by ordering just the upper receiver. You can then order a BM lower separately and have it sent to your local FFL, or just buy a Stag lower (similar quality, way less price)
b) Bushmaster can combine all kinds of details for your upper receiver: different barrel lengths and profiles, etc. In particular, if you don't want a detachable carry handle, I'd go for the A1 sights (Vietnam-style) instead of the A2 sights: way fewer moving parts.
For what it's worth, here's what I did:
--Bushmaster M4 Dissipator barrel on an A1-sights upper-receiver, threaded but no FS (screwed on a 3-prong Vietnam-era flash suppressor) = $515
--CMMG lower receiver, complete w/ A1 stock: $240
Total was still less than a Bushmaster will cost you most places. Would have been even cheaper if I'd used a Stag lower. For slightly more cash you can get your upper from CMMG too, and they have some really cool options.
-MV