Price is ok, that gun is $370 new (add tax), so you save 50 bucks going used, depending how used it is.
I'd go 9mm if given a choice between the two. It's a lot cheaper to shoot. Power between the two is not much, especially +P 9mm.
9 bucks for 50 rounds = 9mm
16 bucks for 50 rounds = 38 super
That being said. If you only shoot once in awhile, the price difference won't be a deal breaker in ammo.