The cheapest: Yourself. It is not a hard thing to do, esp. if you get a garden sprayer.

We used Suburban Power Washing..301-476-9024. They did a nice job but using the clear stain they recommended and they said most people use, our deck came out bright orange! I did not take the day off work so was surprised when I got home. DH wasn't concerned and said it would fade. It was done last June and it has faded but still looks orange. In a few years when it needs to be done again, I will definitely choose a colored stain instead of the clear.

joaniepoanie, I at the recommendation of the store I was using for all my house stuff, I used a Wolman clear water repellant on my deck, and it was exactly that, clear.

I have to wash and re-seal my deck this year, and I'm going to switch, I think, to either Olympic or Sikkens since I've read less than stellar reviews about Wolman, although I was happy with it.