I think when you figure in the free installation of purchased product, they are probably hard to beat. With that they also include the free disassembly of the old parts. Many dealers will offer free installation with parts purchase, but they will charge to disassemble the original parts; Bushmaster does not. If you deal with them on this, ensure the parts are readily available, as many have waited months for the different barrel styles to become available.
Please pass along more information on the Colt model you have. Does it use the small diameter pivot pin, etc?
Another option you might want to explore would be to just get a complete barreled upper minus the carrier group and the charging handle, and then sell off the hbar upper, or just keep it. A very popular upper line is Stag Arms. They can be had very reasonably priced from dealers on this board. You can also buy a Colt complete upper from some as well. I bought a Colt AR6520 without the bolt group for $430.
Bushmaster is a good one stop shop, but with closer examination, you have other options to look at as well.