This is a great novelty joke and it doesn't need much explanation. We all know the type of person who buys the absolute cheapest of anything they can find just to save a few pence.
Its a box containing one real condom with the hilarious words on the box 'Generic Rubbers - For Cheap Fuckers'.
The joke is made even funnier because there is an expiry date printed on the back of the box that reads 'EXP 06-2012. This makes it look like not only have they bought a cheap condom but also one that was out of date several years ago!