Everyone has a way
All contractors charge in slightly different ways. Some by sq footage, some by time and material, some pick a number out of thin air. When we were contractors, we gave an all-inclusive price. The customer never got changed costs unless something really strange was discovered and the customer was informed of the changes and why. So stripping, or cleaning, or cleaning and sealing, was quoted as one price. National average for cleaning/stripping and sealing a deck is about $2 to $2.25 a sq ft. There are many ways to use this average. Some calculate ALL the sq footage. (rails, steps, floors) and charge based on these numbers. Some use just the floor area as sq. footage, then linear footage for the rails, and the amount of steps with/or without rails....Point is, a system to calculate your price, should be consistant and take into account your material, and labor costs. Are you shooting for about $100 per man hour? You should be. You can charge based on any system you like. Many of your dealers have training materials available specifically on that topic. Ask them for the info, ask your fellow contractors, keep yourself informed as to what your area will bear, and don't be afraid to raise your price every year by about 5%.