I go to restaurant depot and spares are $1.60 and baby backs are around $2.20 (Gotta buy at least 6 racks for those prices, otherwise they're a little more). I still choose spares, unless I get a special request, but if you have a restaurant depot near you, it might be worth the trouble of getting a membership card.
Also, thanks on the 2.5:2.5:1 tip. I like competition ribs, but my guests often want fall off the bone. I have missed hitting that texture a few times, and I considered a longer wrapped period, nice to have some confirmation.