Battlefield 4 is £29.99 in the PSN sale but you can get it for £25.80 (bargain!!) using cdkeys.com
If you like cdkeys.com on Facebook you get 5% off all orders (using the code on their Facebook page). Using that code you can buy £25 of PSN credit for £20.80.
Currently they don't have £5 cards in stock.. but you can just use your bank card to add the other £5 to your PSN wallet making up the £30 for the game.
So in the end it comes to £25.80 for the digital version of Battlefield 4. No switching discs or worrying about discs getting scratched!