Any Leupold VX-I or VX-II, Bushnell Elite 3200/4200 series, you can even find some Zeiss Conquest models for under $300 if you watch for them. You could probably even go cheaper on the scopes with Simmons Atec, Weaver Grand Slam, or Bushnell Legend or Trophy series scopes. I don't know what your budget is but don't be afraid to spend $200+ on a scope, I think there more important than the caliber of rifle most of the time.
As far as ammo buy some different factory rounds and see what shoots the best for you. For elk I'd use 165 or 180 grain bullets, but 150's would work if that is what shoots the best for you. Save the brass WSM ammo isn't very cheap and learning how to reload will get you more range time. Make sure what you practice with is what you hunt with.