Only if you don't have NPL color correct the photos. If you do have NPL color correct the photos the cost is $0.75 per 5x7. (Mpix charges $0.99 for a 5x7, color corrected or not, on the same type of Kodak paper.)
If you compare what each charges for shipping, you might see another difference in pricing.
It's entirely possible NPL is happy making a smaller profit than Mpix is. The biggest concern should be about customer service, because any lab will goof up from time to time. How they handle that kind of situation is what I look for in choosing who gets to print images for my clients and myself.
I use the Miller's family of labs Mpix, MpixPro, Miller's, and some other labs for various odds and ends.