My build was as near as possible to a new H&R M14 clone M1A. All parts were NIW (new in wrap) or As-New with original parkerizing. Everything that is/was marked by H&R, was used in the build.
Some of the parts i purchased didn't make the grade when I recived them and were not returnable, so I kept them for spare parts and bought another.
All said & done, without the receiver & barrel, I spent $1,503.45, shipping & all.
An As-New bbl, with no chrome flaking and 0~1 ME & TE gauge cost me $300. It's hard to find such a bbl. I have a spare bbl now that gauges 0-0 but the chrome is flaking on the TE.
If you can't physically inspect each part, then is would be necessary to have a right of return. Even then, shipping is still a part of the cost.
You did not say what grade of parts you were planning on buying, but it certainly has an effect on the cost.