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Just get a hand-cranked winch and bolt it to the wall, and run rope via pulleys to the lifting location. Get the smallest hand-cranked winch you can find, like the kind you'd see used for pulling a tiny motorboat onto a trailer. A person can easily generate 500 pounds of pull with such a winch, and you'll only need a small fraction of that to lift a kayak. Most of my ceiling-stored boats are raised and lowered this way. I've gotten them as cheaply as $10. An electric winch will cost hundreds.
You need two lifting lines for the boat, but if you set things up right, only one line needs to be wound onto the winch. The basic system I use is like this: A single line, guided by pulleys, runs from the winch, up the wall, and either along the ceiling or beneath the rafters (depending on if the garage has a ceiling or not). This rope approaches the location of the boat "end-wise" to the boat, so that it can fork into two parallel branches, with each branch going over a separate pulley for lifting the boat (thus, the two parallel lifting lines are operated together by the one line that gets wound onto the winch drum). It helps to "misalign" the approach of the main lifting line relative to the axis of the boat by just a few inches so that the longer of the two parallel branches does not rub the lifting pulley that is used by the shorter branch.
As long as I'm explaining how I make a hoist, I'll mention that you do NOT want the main winch line to approach the boat from an angle that's much different from being in-line with the long axis of the boat. If the line approaches from the side, the "fork" where one main line branches into two will form a wide "Y", and the location in space of that "Y" will shift back and forth as the boat is raised an lowered, causing the two ends of the boat to be raised and lowered at unequal speed. It will be virtually impossible to set things up so that the boat remains level at all elevations within the lifting range. If you find that you must make the main line approach from the side, you'll need to make use of the kind of complex pulley arrangement of a Harken hoist. For that matter, you can buy a Harken hoist and simply connect the free end of the line to a hand-cranked winch (but try it without the winch first - you may find it isn't needed at all).
I've posted these shots before, but it's not likely that the original poster has seen them. The hoist shown here is similar to what I described above, except that two lines wind onto the winch drum instead of just one.
The winch shown in this set of photos is much bigger than what's necessary, but it was the smallest one I could buy at a store in town on short notice (if ordering online, Northern Tool normally carries a nice, small model for about $10 to $12).