One thing that makes platinum rings so much more expensive than gold is that gold is heavily alloyed and platinum is not. An 18k gold ring is 75% gold and a platinum ring is generally 95% plat. With gold around 1480 per oz. and plat at 1700 you can see where the problem is.
Most white gold is quite a bit harder than plat., so will patinate more slowly, but plat is tougher so will wear more slowly.