Well, you need to have a "wifi mini pci" card installed in your laptop. Chances are it will come with one. If you're going for an economy model, it may state that it's "wireless capable", but not actually have a card. Kinda rare these days I think, since a wifi card can be had for as little as 25 bucks.
Next you need a wireless router. This is where you'll need to research to find a model that offers a good compromise between performance (range) and price. Usually you pay a far higher percentage than the actual increased performance percentage in "hi performance" models.
And finally, of course, the service.
You will have to find out for yourself what is available in your area.
From what I know, DSL is only worth having if your phone company is using optical cable. Our crappy little phone company still uses 40 year old copper lines that proiduce 10-17% noise after a saturating rainfall!
Tedds right with the cost, pretty much no matter what service you choose.