Also depends on when you want to slaughter them. If you don't give them any hay, they'll be thin come the end of the winter, so they'll need a couple of months of spring grass to fill out and be ready to slaughter
But even if you do give them hay, you'd be talking something like a bale a fortnight for 2 hoggs - surely worth it for lovely home-grown meat come spring
However, if you have someone local sells lovely home-grown meat, you may be better off just buying that, of course. Don't forget to cost fluke meds and vaccinations if you do a cost comparison