Do I need to buy expensive toys for my cat?

When your cat is young he will play with anything! In fact he will go after anything that moves! If you encourage it, this playful behavior will continue well into adulthood. And it is a good idea to encourage it, as it will help him to keep healthy and stimulated.
The cat's natural role is as a rodent-hunter or bird predator, so his natural toys are those with which he can pretend to be chasing something. Home-made toys such as aluminum foil balls, tissue-paper balls, cotton-reels, corks, or even a piece of string, are perfectly adequate and he can have hours of fun with these. Outside he will chase leaves and leap around after flies. He can have as much fun with these as with the most expensive toy.
If there is more than one cat in the house, they will often, though not always, play together and have a great time chasing each other and rolling round together. If you have only one cat, spend time playing with him yourself - he will love this most of all!