I found great used M&P45 for $400 cash. If you're not willing to buy a used gun, then maybe lok at the XDs. They are basically the same quality and both manual safeties operate in the same manner, ie up is safe down is off safe. The only major differences I can see is the slide rides higher on an XD and the trigger is a little different than the M&P. The first thing I noticed about my M&P, when shooting, was the trigger pull felt much heavier than the XD and requires me to make almost a perfect trigger pull to get good accurate hits on target. The XDs feels more like a 1911, single action. I grew to like this about the M&P because I get a better practice session even when plinking. Other than that, there's not much difference between the two aside from "new gun" price; the M&P45 being around $650-700 and the XD being around $550.
I hope this helps. Good luck.