I have been using a bucket heater...
and a timer...
...to preheat my strike/HEX/sparge water for my past three beers, and it has cut over an hour off of my brewday, and has saved a ton of propane.
The night before I brew, I fill my kettle (kettle doubles as the holding tank for my HERMS coil during mash) with a full ten gallons of filtered water. I set the timer/bucket heater to turn on 3-4 hours before I plan to dough in. I find the bucket heater can increase 10 gallons of water by about 20 degrees an hour.
During the mash, I leave the bucket heater in the kettle with the HERMS coil to maintain a gentle heat, so the investment kind of serves double duty.
It might be the best $45 I have spent in a while.