it really all comes down to how much you want to grow, and how much you are willing to put into it. having jsut bought all the gear for my setup heres a break down of my expenses for 4 plants.
Good quality tent 3x2x5 tent 130$, 4" fan and carbon filter 180$, seeds 50$, soil nutrients and pots about 50$, 16 26w (actual wattage) cfl bulbs 120$, powercords ducting and other misc expensise, 100$
so its cost me around 600$ to get setup with what i hope will make some pretty plants. im sure it could be done cheaper then this depending on your situation. i bought these things a few at a time to spread my expenses out.
sure it seems like a lot of money but when i look at how much i spend on smoking this will really save me tons of money in the long run.
before you start i suggest you heavily research everything you need because all the little things u need, or need to know really add up, i probably researched for about 2 months before buying anything, there is sooo much to learn and so much information to read through that takign the extra time to make sure u have everythign u need and you know what to do will pay off