CCGs, or to give them their proper name, Customizable Card Games come in all shapes and sizes. The most popular is called Magic:The Gathering, more popularly known as Magic. Its the simplest to learn, and also many other games are based around the same premise. Although it contains the most number of cards, it is possible to make a half-decent deck while not actually owning many cards. Another reason for its popularity is that it can be played by anything up to an entire room of people, if you really want to, but as long as there is at least two people (or if you are sad and lonely you can play by yourself).
They are all great fun to play, interesting to look at the pictures, then recognise them from episodes of Star Trek, or Babylon 5, etc, but as for collecting them. It's fairly safe to say you'll need to rob a bank.
The reason for this is firstly the sheer number of cards, but secondly, the way they are organised. In any one pack of cards you can buy in the shops they are mostly commons, a few uncommons, and some rares. However, given a good third of any expansion is rare, with the other two-thirds equally common and uncommon, it is easy to see that getting all the commons is easy enough, all the uncommons can also be done, especially by swopping your duplicates, but then there are the rares, for which you would have to buy, well let's just say, LOTS of packs, hence spending ridiculous amounts of money.
There are two types of people who buy CCG cards, the collectors and the players. The collectors keep their cards looking brand new, but only need one of each card. The players, on the other hand, may well find they need, say half a dozen, of one particular rare. More money.
Having said that, the best way to play is to borrow other people's cards, play in tournaments, get really good, and hence win loads of cards without buying any. Difficult, but not impossible.