1st of all, it can not be installed over a plywood substrate if it is truly plywood...Even if cdx grade...good on one side..With that said, I am guessing that a new underlayment like multiply is being installed and then the vinyl. If so , the price seems fair. Sounds high if no sub floor is being installed. Plywood does not get prepped, sub floors do.

Thanks. They were including an underlayment since the original plan was to lay the new floor over the self-stick tiles, which I've removed. The existing plywood sub-floor floor is stamped Sturd-I-Floor, which Mannington seems to say is OK if not damaged ("2010 Professional Installation Handbook", p.10), which it doesn't appear to be. I want to re-use the trim and thresholds so installing without additional underlayment seemed an advantage. Whatever, they're the pros so I'll do what they say since you've re-assured me on the pricing.