It's easy, but tedious. The ceiling will be no fun. Also, "cleaning" or
"sawing" the current grout with a grout saw won't be much fun either, but
not really that bad at the end of the day. Go take a look in a DIY tile
book at your local Home Depot, or the library, and you'll see how to do it.
Sometimes people give high quotes like $450 because they don't really feel
like doing the job, but for $450 they get over those feelings. It doesn't
mean it will excite them into doing a better job than you can do though.

I highly recommend using a grout cutting bit in a Dremel tool. Using a
grout saw would be home repair hell.

BRW