It's expensive to have it rebuilt so I would look inside it for evidence of brake fluid (likely there is...) and test it to see if it holds a vacuum and make your decision based on that and the difficulty of removing the booster later on if it needs rebuilding.
White Post Restorations in VA will rebuild the booster and cylinder for something north of $400, IIRC, mid to high $400's. They re-sleeve the MC in brass and thus provide a lifetime warranty , but they won't warrant the booster if they don't rebuild the MC since leaks is what kills boosters most of the time.