Of the mainstream; 338 lapua and the 338 Rum or 338 edge are all real close in performance, obviously the rum gives a little up in velocities.
Lapua brass is about $230 per 100
300 rum brass for the edge is about $85 per 100
338 rum brass I can't say for sure but probably in the $80-90 per 100.
The 338 win mag would be a step down from the above, This is a good round and if your not intrested in launching 300 grain bullets, it is probably a reasonable choice with bullets of 250 gr and less. I would guess that brass is running somewhere around $60 per 100.
Not much else is mainstream, 338 federal? 338-300wsm? 338 Allen mag?