HM I feel your pain. I just bought some deck stain/sealer the other day. It takes about 5-6 gallons to do my deck. I have to admit, this deck sealer stuff is a scam. They say it will last 4-5 years,,, HA! Try 1, maybe 2 years, that's it. Plus, my deck has actual decking boards on it, not 2x6's or 2x8's. SO, as anyone knows, when you have decking boards, over time the boards warp a little. SO when you roll on the sealer it pools up in the center of the board and ends up looking like crap. Plus you lose half your sealer through the cracks. Last time we did our deck we used 10 gallons. Not this time. I told my wife (who has been heckling me to get this done) that we are going to brush the entire deck because I'm not spending another $152 for 5 more gallons. Instead, I bought 2- $15 brushes that are 4" wide so I think I used the saved money wisely. We've been fortunate to have a very nice, cool June so far... this week is hectic however- so we'll have to wait till next week for the deck. Knowing my luck, it'll get up to 105 degrees next week.
By the way for any of you out there sealing your deck- Thompson's water seal DOES NOT WORK. IT'S CRAP. DO NOT WASTE your money! That stuff literally is AWESOME for approximately 6 months. Then wears off. I have not tried Cabot, but heard it is good. I personally us Olympic Maximum. This stuff does a good job and will last close to 2 full years. I do recommend washing your deck first as the sealer will absorb better and your deck will look nicer when it's all done too.
My next deck (at the house we will build in the near future) will be complete composite wood. Yes it's expensive, but it's worth it. Power wash it twice a year and boom, you're done. :)