do a bit of market research around your area, ring a load of valeters say 4 to 8 different companys and get a quote for the vehicle in question and that will give you an average of what people are charging in your area. prices up and down the country vary quite alot due to location and type of service offered etc etc.
if that was in my area id be charging around £100+ mk due to the size of it and the amount of stuff that will be used on it etc etc but joe bloggs in another area could only be charging say£70/80.
quoting is really difficult when your not seeing the car first, ive had situations where ive quoted then got to the job and found myself right up against it because the car was an absolute shed when the customer said "oh it only needs a quik flick over its not that dirty" and it needed easily 1.5/2 hrs extra spent on it.