you can start off as small and cheap or as large and pricey as you really want.. but here's a small list of some minimum things that you'd need to start a simply one plant grow..
several of the largest actual wattage cfl bulbs in the 6500k range for vegging and several of the same wattage in the 2700k range for flowering.. bigger cfl bulbs can run around 5 -10$ per i'd say just for an estimate.. say you get ten of them, that would take you to around $100 give or take just for lights..
or you could drop some more $$$ and get a decent hid setup from a place like htgsupply and get say a 250 watt setup for about $250 everything included..
http://www.htgsupply.com/Category-GrowBright-Grow-Light-Systems.asp..
than you'd need some soil and pots or containers.. i can pick up a big bag of fox farms ocean forest for around $15 or so from a local hydro store..
nutrients can also run as cheap or as expensive as you'd like, but i'd say about $50 or so for a pretty complete line of nutes like the fox farms trio of big bloom, tiger bloom and grow big that will last you several grows atleast..
lastly you'll need some seeds or clones... if you want to save money, you could always use seeds that you pulled out of some bud that you bought, or you can spend some money and get some better genetics and therefore pretty much a better end product for as lil or as much as you'd like to spend once again... sannies seeds has some really nice stuff that you can pick up for around $50 or so for ten seeds, or you can check out the attitude as they have tons of breeders who's prices spread the complete range from say $20 or so for ten beans all the way up to say $600 or so for ted seeds.. expensive is not always better when it comes to seeds, so it really pays to do some homework when it comes to what seeds you buy and where you buy them at..
opps, i almost forgot a small oscilating fan for air circulation.. i'm sure you can get a decent one for $10 / $20 or so.. there are tons of other things that you could buy as well like a ph meter, ppm meter, ph up and down, lots of different nutes, bigger better lights, carbon filter for smell, etc... but what i listed is basically the minimal that you'd need to start a small grow.. once you have that, you can always buy more as you go along and figure out what you're missing and what will make your grow better as you learn and read..