FWIW, that doesn't sound bad. I'm south of you by a few states, I had beein looking at the M&P and the Glock 19, it seemed like the M&P was supposed to be a little less expensive w/ std sites, but w/ the night sights, they got closer in price...
At some of the stores here, they were trying to see the M&P for mid $5XXs, and the cheaper SVE for $4XX+, but I see online dealers (like budsgunshop.com) selling it for $400 + Shipping + FFL, but I still see other stores online selling it for $480ish...
As for the price difference, the ones selling it for $480ish have a similar price, whether std or compact, but I noticed buds had a $47 premium on the compact, so maybe fresh shipments from certain suppliers are coming w/ a lower price on the std model? I'm just guessing, only beein looking at these for a few weeks, and ended up leaning towards the glock, only because it was hard to argue w/ the way the rounds hit the paper for me, despite the M&P feeling better in my hand.
So, IMO, if they're offering you $400 out of the gate, that's not bad, you could do worse, but again, I'm not expert. As for the night sights, I don't know how much more that should be w/ purchase, or added later, I did notice the few online sources I went to just now did have $500+ prices for NS on that gun, not sure if Bud's had night sight options or not.
Good luck whatever you do!
Karz