They exist... about $60 for a B router and about 90 for a G router. What do you want to be wireless? You're computer or the PS2? The PS2 being wireless will cost more because you will need an wireless adapter (about $70) or an ethernet bridge (about $90). Having the computer wireless will cost you about $40-50.
So figure a price point of around $100-160 total depending on what you want to do. Of course both being wireless will cost more.
I personally at home have my Desktop, Laptop and Tivo are wireless while my XBOX is connected via ethernet to my router.