Forever 21 has the best and cheapest solid color t-shirts! I own black, yellow, and olive green. They are only $4.80 each, and they are good quality and fit wonderfully.
If you're looking for colored t-shirts for crafts, go to Michaels. They have a wide variety of colors, such as lime green and hot pink, and they cost only $3-$5 each. When they're on sale, you can get 5 for $10.
You have some pretty good taste in music :)
Hot Topic usually has all sorts of band shirts for about 10$ each. I personally like to buy all my band shirts at HMV, where they usually have Buy 1 Get 1 Free sales.