Contract card

I'm a little confused with contract cards..... I haven't bought one yet, but do I have to buy a card for each player to extend their contract???? Are they worth it or is it better to just try and buy a pack and get one there and if so which pack? I'm trying to do this all without adding points with money.

Thanks guys!

It only extends for one player that you select, if you have a gold or platinum card you want to keep, you go to the weekly deal and find the offers that are always there and buy one for a player.