Thats the main issue. Your cost analysis excludes brass.
Where will you get the brass and how much will you pay for it?
I get once fired 300 win mag brass for dirt cheap at the range.... where would I get 338 brass? Buy brass for 2.50 each from lapua, or buy expensive ammo and reload.... oh well. anyway.
I have seen once fired 338 brass on the EE here for $1.35 each. Not too bad, thats where I would start.