I get ALL my bras from Victoria's Secret online in the clearance section for really cheap! I don't pay more than $25 for mine. They fit me sooo well and last a long time if cared for properly. I hand wash or use the gentle cycle on mine and never ever throw in the dryer. I hang dry them and place them facing up in my dresser so it won't get squished and change the shape of the cups. When a bra comes out that I want, I wait for it to go on sale and 9 times out of 10, it does. I can't justify paying $50 for a new bra when I know it's probably going to go on sale in a few months (or less).
Before college (like 5 years ago), I used to buy my bras from this place called VF Factory Outlet. They are located at random outlet malls. They have decent bras and they go on super sale sometimes ($3 or $5 each). Some of the brands include Lily of France, Maidenform, etc. However, the quality isn't as great and they don't last nearly as long. If you're on a budget, you should check those places out.
Some other good places to check out are Marshalls/Ross/TJ Maxx. They have a lingerie section and usually have a decent selection of bras. Sometimes you find really good ones there (Calvin Klein etc.) for quite a deal. Always always try on the bras even if it's in the size you normally buy because different brands run big/small.