My only comment is that we have been doing a fair amount of color sealing recently on a number of different kinds of tile, tile widths, area sizes and different types of grout, some of which needed to be
stripped. For instance, on a floor that had 6" kitchen tiles that had been previously sealed I charged $6 for the whole thing (including stripping, cleaning, color-sealing and color enhancing) and lost money because of the time required. In some cased the ventilation is so bad that the stuff will not stick to the grout without a lot of prep, blowers etc. Or maybe the grout is very shallow, or the tiles grab stuff and a lot of razor blading the edges is necessary. Other tiles are pretty easy and straight forward. Testing with custom colors also takes extra time. We also do small tiled vestibules in a large apartment complex near here and the area is typically only about 50 sf., for which I charge min $195.00 regardless of price per square foot, which takes into account set up time.
I always (since taking John's marble restoration for businesses class) always estimate time, figure in 3-4x labor costs to get to a 66%-75% margin, add any high priced materials and then work back to what the competition might charge and also estimate how much extra time my guys can put in before I start to lose money or at least not make enough that I would think is worthwhile. But as a quick calculation on a fast job, I think Bruce at Grout Perfect told me that really fast guys can do 900 sf in a day (not my guys!) and if you assume then say $30 per hr for two people times 8 hrs times 4 (75% margin) you get to a little over a $1.00 psf for sealing only. But, as I said, I have run into many situations that would significantly increase that price.