yeah.. I had to save up SP though... I have no real money lol

I bought and

- Oh, so you can actually buy them in shops from other users?

You can, but they can be damn expensive, it's easier to get them directly from the creator or the Cash shop

http://subeta.net/ushop.php?act=dosearch&itemname=500+Credit+Gift+Card&type=shops

^or you can buy the gift cards, which is what I did (still expensive)

Yeah, you can pay sP for CW's either by getting the CSC cards (as previously mentioned) or some users may sell them for sP ;) I personally think it's much easier to use real money. You don't have to wait as long, trying to save up! I personally have quite a few CWs :)