I find the thought of a motorised reel a little scarey - goodbye to fingers and all that. Maybe a sprung loaded one or possibly a geared one to give less turns on the reel handle?
The problem with a spring loaded one is that they only extend 20metres and they do break a lot. I have a friend who repairs plenty of them, time, after time, after time.
There are electric ones which I think Matt or NWH suggested. They are very expensive but probably cheaper (in time saved and effort) than trying to build a DIY one.
Just a suggestion.............. instead of using a gardiners, WCW, chic cleaning, etc, popular styled, metal framed, hosereel with a small drum fitted, source another hosereel with a much larger drum which requires less winding to reel in the same length of hose to make life simpler.
I use an Ionics hosereel and although pricey, I really can't fault it. I've had it for 5 years and it makes reeling in 100 metres of hose much simpler than using the standard, popular hosereels sold by gardiners, WCW, chic cleaning and the likes.