What kind of possibilities do I have to make my PC wireless ? And what are the costs, about ?

Lots of possibilities and it is cheap, what do you want to do?

you can buy internal Wireless network cards and external (USB) 'dongles' - you will be looking at around 800-1,000b for these.

I use a internal 'card' style one for my PC at home, works very well and im connected nicely to my wifi router. I also have a USB dongle style one which works just as well.