Since I'm sitting here studying for my acoustics test, I figured I'd say a thing or two about tuning a room. Obviously, if you just listen to music, this probably isn't very important to you and would cost too much money. But for anyone that's mixing, having an acoustically treated room is more important than the speakers you have. What's the point in buying high-dollar speakers if your room is totally skewing everything you hear?
For anyone working on a budget, it really doesn't cost too much money to get a good sounding room. Really, all you need to worry about is the reverb time of your room, adding bass traps, and adding a diffuser. There are some simple formulas for finding out what frequencies you need to work on trapping, but there is a nifty calculator at MCSquared.com that will let you cheat a little. It calculates the axial, tangential, and oblique modes according to the room dimensions you give. Most people will argue that unless you are trying to treat a concert hall, axial room modes with be enough for you to work with.
As for finding the reverb time.... sorry, I don't have a calculator for that. That's some math you're gonna have to do by hand. It's not really that hard, just time consuming. It's also a pain because unless you're straight up building your room, you have to find out the absorption coefficient of whatever materials are already used in your walls, ceiling, and floor. Then you have to find a new material to add that has the right absorption coefficient to compensate for that damage that your pre=existing materials are causing.... it's a pain.
But anyways, if you're interested in it at all, look a dude named Ethan Winer on youtube or go to his site, RealTraps.com (I swear, it's not what you think!). I wouldn't suggest buying his product unless you want a bunch of gawdy panels all over your room, but he has some good videos that will explain how to tune a room. If you really want to make a purchase, I'd suggest Auralex (although it's uber expensive)
If you're really brave, try building all your traps and diffusers from scratch! Anyways, I'm gonna go back to studying.