Regrouting can be a very laborious job if you don't have the right equipment. It is very labour intensive and can be a very dirty job. I have recently done the toilets in a night club and I can honestly say I think it was one of the dirtiest smelliest jobs I have ever had to do. I thought I had put in a high enough quote not to have got the job but I got it anyway.

The next time the quote for any public toilets will be 50% higher again.
Gary (Highlander) is right when he says you get quicker. Initially you are frightened you will damage the existing tiles but as you gain experience you get quicker. Natural stone is easier for me because I am in a position to repair any errors. With porcelain and ceramics you have to be even more careful unless there are spares
If any of you get to quote for such a job don't be frightened to charge and allow yourself a day or so longer for cock ups. The first time it will take longer than you think and as Dean says sometimes it can be quicker to retile.
Kev