I can buy Glocks NIB with a little poking around for $450. Best price I gave found on a P320 is $505.
Not a huge difference but still a difference.
I never said there was no difference, merely implied it is not what I consider to be a large difference. I responded because when people think of SIG they often think of the prices of the classic P-series pistols which typically run $800 for the basic models and easily to $1000 if we're talking an "Elite" or "Equinox" model (local prices, not online). That's a substantial difference, to me, as opposed to say a Glock.
Prices also do vary locally. Locally I cannot find a Gen 3 Glock for lower than $500 NIB and a Gen 4 Glock NIB for lower than $550. P320s with night sights tend to run around $580 here. When considering that you're getting a pistol with night sights as opposed to one that doesn't, the price difference for me is negligible at the local level. As you've pointed out, there are other options for buying and likely different prices by region too. Were I able to buy Blue Label Glocks that would also be a different story.