Typical Gunbroker prices are around $700 for the .45 variety
As for your questions about loads, it is the other way around. The Redhawk is a stronger gun than the Blackhawk. Anything the Blackhawk can digest can be shot in a Redhawk, but not necessarily the other way around......that being said, any load that would not be safe in a blackhawk is probably way overkill for anything in the lower 48.