In our case we use our own farm, it pays for itself and we have it always without being worried about surprise costs even when we have to re-render any that had a problem or an error.
In your case, probably Rebus will do the trick, we used some time in the past and it worked ok, the problem was the cost estimation, it turned out to be more expensive than what their calculator say, but for still it could be more precise, I don't know, it's a guess.
Cheers!