When The Last of Us comes out on PS4 soon, it'll be sold for $50. To help alleviate the cost a bit for previous owners of the PS3 version, you can trade-in your old copy at GameStop starting July 27, and pick up the PS4 upgrade for $25. You have until August 2 to take advantage of the deal.
For reference, new copies of the game are going for $25 on Amazon and eBay at the moment. You may not like GameStop, but this is a better deal than Sony is offering -- which is to say nothing at all.