I have "painted" them with black RTV before, and it has worked, but it's a very very very temporary thing. Eventually it will fail - and probably soon. Do it, see IF it helps, but don't plan on it being permanent.
Another cheap band-aid you can do for old carb boots is a wintergreen oil soak. Google it. It also may HELP you eek a bit more life out of them.
As Dods said, once they reach a certain point there's not much you can do. Replacement is best, but I certainly understand having to make budget repairs.