Downr@nge, they won't let you out the door once you flash that Jersey ID. A handgun can be shipped to a licensed dealer who holds an FFL (Federal Firearms License) when purchased out of state. You'll have to OK that with the dealer before hand and negotiate a price. Perhaps showing him someone else's price might incline him to lower the price to something reasonable rather than the $31 off full retail being offered.
My first M&P was on sale for $550 but I had a discount coupon (Cabelas) for $75 off making it a good deal. There was also a $50 mail-in rebate (and there still is).
My second was a used but like new 9mm compact. I paid $425, a bit much but I wanted one for the wife to try out.
The third was a 9L which runs a bit more than the standard M&P. I paid $530 for that one through a local gun shop I frequent.
The 40/357/9 M&Ps in Full Size and Compact all tend to run the same size, the Long, Pro and Pro Series will all be more as will the .45ACP.
Have a look at the following to get an idea on current pricing, keeping in mind these are internet prices and may be less than a small local store can offer:
http://www.budsgunshop.com/catalog/advanced_cat_search.php?cated=26&manufacturers_id=31&ITATR_list%5B1%5D=1914&ITATR_list%5B2%5D=&ITATR_list%5B3%5D=&ITATR_list%5B4%5D=&ITATR_list%5B5%5D=&ITATR_list%5B6%5D=&ITATR_list%5B7%5D=&ITATR_list%5B8%5D=&ITATR_list%5B9%5D=&ITATR_list%5B0%5D=.
If your local dealer is willing to do a transfer, it will generally cost you an additional $35 plus what he charges. I would push for a better deal or perhaps take a drive to a smaller town in-state.
One note about the M&Ps and ammo cost, the 40 S&W isn't much more to shoot than 9mm and provides much more flexibility as several barrels are available to change calibers. You can buy a 357Sig barrel that will work with your 40cal. for about $80. You can also buy a 9mm conversion barrel for about $150 that will drop in and needs only a new 9mm magazine for proper function. If you buy a 9mm anything, you will have to purchase an entire slide assembly AND magazines to shoot 40/357. The 45 is not interchangable with its smaller siblings.