When a re- word is not specifically listed in dictionaries, it's still a valid word, if it has a comprehensible meaning. Recosting obviously does, so the only remaining question is whether the word is too rare.
I was slightly surprised that there are not more examples to be found of recost / recosted / recosting, but there are some examples, mainly in writings on project management and the like. For example, an article about wind farms in the British Observer quoted an analyst as saying "Many are now recosting their plans..."
Based on the evidence I've found, it's a borderline case, but the meaning is so obvious that I think it ought to be allowed. (And it's probably no rarer than sectoring.) For the sake of consistency I'll insert all the inflected forms, recost, recosted and recosting.
There's no charge for that, cb. No - wait - on second thoughts...
