If the cost of boneless is less than 150% of the cost of bone-in it's cheaper to buy boneless chicken thighs.
Has anyone else looked into this for other cuts? Obviously I'm not going to be able to know the yield for everything without trying it, so I'm just sort of looking for a rule of thumb for shopping.
The restaurant terminology for this is 'edible yield' - basically the amount of food you get per pound purchased. Lobster in Maine might seem cheap at $8/lb live in shell, but you get about 25% edible yield, which means per oz it's still more expensive than a $12/lb t-bone steak (edible yield of roughly 80%). You can find charts that estimate the edible yield on everything from t-bone steaks to whole Salmon.
..and to echo the other posters, the bones and skin have value in-and-of themselves. Many dishes taste better using bone-in thighs, and you can use the bones and scraps to make broth or stock.
Another approach is simply to compare how many servings you can get per pound of various ingredients. For example, with 1.25-1.5lbs of bone-in chicken thighs I can get four servings of most braised chicken recipes plus a quart of stock for soup or risotto later.