sports bras....I hate to say it, but if you NEED support, then any place where you can buy food, dishes, cards and that has a dollar bin isnt where you are going to find it.
Sports bras that are cheap are meant for people who need cheap support.
If you have a bountiful pair, then ordering online is about the only way to go. Running stores and sporting goods stores often carry good sports bras but the selection of sizes is limited (although you will have more luck finding a 40 DDD than a 34 DDD or a 40B). Enell, Champion and I hear nike has a new one all carry bras that will support. Good places will take returns if you leave the tags on to try on, although you may get stuck with shipping
I run...there is no greater bounce test than that! I know bras