All SSD's have been dropping in price lately. Newegg recently had a 2 day sale and the Samsung 830 256 GB was on sale for $189. While the M4 512 GB may be cheaper at present I'd be willing to bet the 830 512 GB will be following suit with the price continuing to head south. As I, and someone else mentioned earlier, Apple is using Samsung drives in the 2012 models. If a buyer is patient, watches the boards, and does a bit of research good deals are out there to be found.
Not taking anything from the Crucial M4's, but I personally feel the Samsung 830 is the faster more reliable hard drive. It's all a matter of personal choice.
Enjoy that M4. I know it rocks in the MBP too!!