Screw a grow tent. Buy $20 worth of 2x4's, and sheet of mylar.
It should cost you max $30, and you can customize the size.
100 feet of mylar ($1.29):
http://www.texashydroponics.com/shop/product.php?productid=685&cat=223&page=1
Also, you are going to have to drop $150-200 minimum, on lighting, and that is IF you find a good deal on Craigslist. A 400watt MH/HPS setup will run you right at $300 brand new and air cooled.
Dont forget about air stones, air pumps, normal fans, ventilation, net cups, hydroton pellets, rockwool cubes, nutrients, pH up/down, pH meter, etc. You have ALOT of cost before you get into the stuff that is actually gonna make them grow.
Trust me, I tried to do it for $700. But to get the results I want, which is about 20-30 plants, I have about $2000 invested. $100-85/a plant you want to grow. And I am not being a cheap...I am running CO2 and the works. You might not want the results I do, but that is what you are looking at.
Of course, after the initial grow, it will pay for itself, and plus about $3k after 1 harvest. I plan on running a perpetual setup with a total of 80 plants, once this grow is done.
The best bit of advice I can give you:
"Until you get your atmosphere under control, you are just pissing in the wind."
Basically, until you get your temp, air flow and humidity are dialed in with lights on, you are just wasting your time. 76deg, 40% humidity, and good air flow. It isnt hard to accomplish, but until it is accomplished, there is no point in growing unless you want hermies, males and generally fucked up looking plants.
You shouldnt have a cheap mindset. That is the LAST thing you want. Get in your mind how many plants you want, how much you want produced(ideally) and your grow room size. Then start from there, and dont forget the small cost(net cups, hydroton, pH up/down).
