I just bought another Sig P229 on GB. The same dealer (Chestnut Too) had an M&P 40 with still working night sights, & a starting bid of $345.00. Shipping was free & no extra charge for credit cards. Fast, courteous service, too. I was REALLY tempted, & I already have both a 9 & 40 M&P. The gun was relisted & has 20 hrs to go, if you're interested.
There is a flood of ATL PD marked guns around here (I think they switched to Glock). Dekalb Co Ga PD (DKPD marked) just swapped out MP40s for newer MP40s. The replacement guns are not PD marked . I bought my "old" duty MP40 for about $330 (w/ 3 mags and night sights)
I was looking around on the web last night for some training and one of the LGS that I never go to had a bunch of Block .40 police turn in for $399 as well. Seems to be the going price in my area.