I originally designed this thing as a test for using Proto Pasta's high-temperature carbon fiber filament, but the test print I did in plain old PLA actually works pretty well. PLA is not really food safe because you can't clean it in really hot water, but if you are just pressing garlic with it (and not, say, meat) and the rinse it well afterwords, you probably won't die.
UPDATE: In addition the attractive classic version with the round well, I've added an easy-squeeze, easy-clean version with a square well.
I used 4 perimeters to make sure it is really sturdy. You should also print it pretty hot and slow to make sure the layers fuse completely.
For the classic round version, use the files body.stl, lever.stl and plunger.stl. For the easy-clean version, use the files body2.stl, lever.stl and plunger2.stl. Note: you will need to use a raft when printing plunger2.stl.
I used 0.25" outer dia x 0.625" long nylon spacers for the pivot pins. You could also use short pieces of 0.25" dia brass, aluminum or steel rod. All should be available at most hardware stores.