You may not want a pistol grip with the Mossberg. It makes manipulating the tang mounted safety harder. The Maverick may be a bit better in that respect.
I'm not much of a fan of PGs on Shotguns, but if you are that is something to consider.
The cost difference of the Maverick is largely due to a lot of the Mexican manufacturing of parts for the factory in Texas. It saves on labor cost, but the design is just as deathkricket said, mostly Mossberg 500. Fender uses a similar strategy in cost savings by opening a guitar manufacturing plant in Mexico to make their standard Stratocasters and various other guitars that they offer, so that they can capture a segment of the market who would be priced out of a USA Standard version of the same guitars.