Some people aren't getting the fact that with a 400w light in a small space you will need a noisy 4" or larger exhaust fan and a good fan to circulate air for the plants or you will cook the holy fuck out of them. You will not pull this off with computer fans or anything running off a wall wart.
If you want cheap and good look for used 4-6" can fans on ebay or craigslist for your area, or look for squirrel cage fans 4-6" used also those are powerful but cheaper.
You can even salvage big 6" squirrel cage fans from used Jenn-Air downdraft ranges or similar probably. It's a seperate part from the stove and you can just wire it up to the wall or better yet wire it to a speed control. Many people can tell you how to hook up two wires to two other wires with wire nuts and how to turn the nuts clockwise to tighten them too in case you are afraid of just getting a fan and having to hook it up to a cord/plug.
I use magnetic 1kw ballasts and some have a hum but none are the main source of noise, and I don't even have to exhaust my rooms with a high speed exhaust fan I'm just using floor fans and a/c. I could easily silence them if I wanted too work on it though.
400w ballast kits are $50 again so simple to wire... 400w warehouse ballast hps's are everywhere for like $50 ready to just connect a plug. Halide ones are average $25 on craigslist. You can remote wire them, there are threads already showing how to do these things with pictures if you search or just ask in a new thread when you find what you want and you'll have the answer in no time.
I'm the king of cheap... For a long time I've been collecting the most budget stuff I can find in bulk to make up a 20kw grow and I have a fraction invested of what any sane person would say that setup would cost. I'm not running that yet, I'm preparing to jump on the bandwagon the second the laws change locally though. I'm going to cash in big and then buy better stuff. You will find whatever you buy will likely give you more than enough return on your investment that you don't need to even think about it. How much is an ounce where you live if you had to buy one? You can get used 400's for the price of an 1/8th and 1000bulbs.com will give you cheap bulbs.
Hell I have a full case of 14x 400w hps bulbs brand new I don't even need anymore. They are only selling for $5 ea on ebay, so I'm just letting them sit here. Screw it... They're cheap.
