Reloading supplies are readily available for both the 458 SC and the 50 BW.The cost for reloading each is about the same.
The ballistics are a toss-up,both are really only good for around 200 yards,after that the bullets are falling like dropped bricks.
I prefer the 458 over the 50,there is a much larger selection of bullets to choose from with the 458 since it uses the same bullets that any .458 caliber rifle can shoot.Handloading either cartridge is the same,there's nothing to worry about with a shouldered case over a straight walled case.
As long as you don't push the upper limits with your powder charges,the brass will last many loadings.I have some 458 Starline brass that has been loaded over 10 times,and it's still good to go for several more loadings.I have only needed to trim those cases about every 3 firings.
Everyone wants to say " I gotta 50 cal",and there's nothing wrong with the AA 50 Beowulf,if that's what you want.But,I prefer the 458 SOCOM over it,and trust Rock River Arms and Marty ter Weeme (The 458 SOCOM inventer) a lot more than I do Bill Alexander (Alexander Arms).
And you can have a Low profile gas block with the 458.Mine is a Mid-Length with a Low profile block,and a full length Hogue handguard.
I paid $750 for the complete RRA upper,just the way it looks.