The rest was bought in stages, with the most expensive piece being the complete upper for $415 + shipping (but you can buy the parts for about the same amount of money separately - barrel/upper/bolt/forward assist/charging handle/gas block/tube). Everything but the lower (as this is considered the "gun" by the BATFE) can be purchased without any FFL involvement and shipped direct to your door.
You could easily get this done for around $1,000 for all the parts, or as low as about $750 if you can find a kit for everything but the lower.
OUT OF STOCK.
OUT OF STOCK.
OUT OF STOCK.
OUT OF STOCK.