I have looked at dozens of M&P pistols - I own 3 of them - have never seen one with factory night sights -
S&W web site does not even list a SKU for the M&P with factory night sights. But does have the night sights.
390100000 $52.50 X FRONT SIGHT (NIGHT)
390790000 $123.90 X REAR SIGHT (NIGHT)
So for only $176.40 plus shipping and TAX (which S&W charges on every order) my guess $200 you can get the night sights - maybe another $25 to have someone install (from what I have read the rear sight can be a little bit of a PITA)
$225 seems like a lot for night sights -
Crimson Trace has a laser for the full size M&P - I tested one at a gun show - pretty cool - it raised the price of the gun $200 (list price is $329) - I would guess the laser for the compact model will be out soon. It just replaces the stock back strap.
http://www.crimsontrace.com/Home/Products/...45/Default.aspx
Edit - I have considered buying just the front night sight - even though it seems like in most SD situations (close range) night sights would not be all that important anyway - even in low light - having better visibility to the front sight would be a good thing.