$500 seems alright....you to have to account for the fact that there arent that many pressure washer guys out there during this time of year....i say go higher. I NEVER go under $7.50 per square foot, and thats on an easy deck. i say you should shoot for $9 to $10 per square foot. easy way of increasing your profits is to not use any chemicals. just pressure and a little bit of your time cleans EVERYTHING.

GOOD LUCK!!!!!!!!!