I would suggest looking for a herp show in your local area. You will be able to find some great deals there.
You can also try Kingsnake and the For Sale Section here on these boards.
You could also look around, maybe post a wanted on craigslist, for a breeder in your local area.
Before you buy your first snake, make sure you have a look at all the sticky posts on this page.
It would also be a good idea to learn a bit about some of the morphs through the stickies on top of this page before heading out shopping.
You can get a ball python inexpensively at a reptile expo, but the set up will be expensive. If you go with a tank, you will need tank, hides, water dish, lid, thermometers, thermostat, heat pad/heat lamp, substrate, and a something to measure the humidity.