I used to shop ebay for miscellaneous gun parts for my p250s then p320s when I switched over. Prices were reasonable and often there was free shipping. When I made the transition to the p320 I put a spare 250 slide, barrel, guide rod and spring up for auction. The bid went for $300! That was three years ago and since that time I have watched the auctions for p250 and p320 stuff out of curiosity, I really can't believe that stuff is actually selling for the prices that are asked, like $200 for an FDE grip module.
My point is that the lack of availability of items through Sig or the traditional websites like TopGun or Osage County Guns has driven prices up like crazy. Sig's prices on exchange kits are nonsense. Recently when exchange kits for the p320 were listed for $400.99 at the Sig Store, I bought two CPO p320s, a full-size and a compact model, for $399,99 each through gunbroker.com. Got everything that comes with a new one, including night sights, except the case. Got the CPO "red box" instead. One year warranty.
Crazy times for Sig lovers.