Cheri writes:

Since I know nothing about home repair, is the cost
excessive, number one, and do I have to let him come back?

No. Don't allow him back. You will not get it done on the 2nd try.

Sounds like this guy is in the business of stonewalling disputes with
suckers, not actually delivering value for money.

There is no magic way to "doctor" grout. There isn't even a good way to
remove and replace it.