In a year a pig will eat around 900 to 1,000 pounds of feed and at $15.00 per 50 lb bag you would need around 18 to 20 bag of feed.
So let's just say that you'll need 20 bags of feed per year for each pig and at $15.00 per bag that would cost you $300.00 per year to feed just one pig.
That's not too much however you'll likely be better off just buying bacon and pigs meat in stores if that's all your raising the pig for.