The scope would be the same as a scope for any other rifle that you would want to shoot at similar range. But yes, good optics are always expensive, whether for a .22 or a .50, if you want a quality optic, it can cost as much or more than the weapon you plan to put it on. This case is an exception, as the weapon is so expensive.
The mounts and rings might be more expensive, as they would have to be able to resist a lot of recoil without loosening or moving. Badger makes rings specifically for .50, and they aren't much more expensive than standard Badger rings. Though Badger rings in general being top of the line, they are pricey by a lot of people's standards.