How much does a box of shells cost for a 12 gage mossberg maverick no 88?

Cheaper "promo" shells and bulk target shells from places like Walmart can be as little as $4 for a box of 25. Those are always smaller shot size target shells, though. Specialty ammo like 3" hunting slugs can be as high as $20+ for a box of five.

For all around target shooting and backyard fun, go for a medium shot size #4 or #6 in a 3.25 dram load. You can expect to pay in the $7-9 range. For home defense, a larger shot size, #4 shot or larger is the usual suggestion. 00 buckshot is the most common favorite and it usually runs $2 per shot or $10 for a box of five shells.