There is no specific set cost due to a multitude of variables possible with the cleaning. Please let me know where the slate is located, and size to be cleaned and sealed? Also does the cleaning require removing and excess grout? And lastly will you be providing the sealer or the person doing the work? With this information I may be able to give you a fairly good estimate.
Dennis (cut2it)
A good and thorough cleaning, plus drying time, and applying two thin coats of good quality sealer, including cost of sealer should run no more than $180.00 to $220.00. Also the first coat of sealer needs to dry before applying second coat.
C&onstructi&on C&onsultant
Over 40 yrs. as General Contractor for new const. & remodel - retired with time for you.