Late to the party, but the Restaurant Depot around here sells beef short ribs for about $4-5 per pound for the racks with four bones, and $5-6 for the racks with three bones (which are bigger). They're sold in packs of four racks, and they usually cost around $75 a package for the smaller, $100 for the larger. Each rack feeds a couple hungry people, so you're looking at 8-10 servings in a four-pack. I usually take two, wrap in plastic and throw in the freezer. Oh, and despite the "short" in the name, these are massive dino bones.
If you're planning on cooking beef ribs often, try to find someone with an RD membership who can get you in. Totally worth it just to be able to select whatever rack looks good and has good fat marbling. With a butcher you're taking whatever they give you, it'll probably cost more, and you may have to special order it.
Short of that, your grocer may have short ribs cut into smaller cubes with the bone still on. Kroger, the grocer around here, does. It's actually a good way to get started or experiment with beef ribs without committing to the whole rack. They don't take nearly as long to make when cut up this way. (I started with the cubes and it took six hours. Now I spend about 10 hours smoking the racks, without wrapping in foil.)
Here's a shot of my best work so far.