Electric tillers are available in a wide price range. The heavier use gardens might benefit from a better tiller, designed for longer use. But, for a small garden electric tillers can be found at reasonable prices.
Remember, the wider the cut the less walking for the gardener. That having been said, a wider cut requires a motor built for a greater load. For my purposes a foot wide cut is fine. And a six to eight inch depth is enough, since I plan to add garden soil to the tilled area, thus building it up. So, even a long carrot would thrive with an eight inch tilled bed and four inches of added soil building things up.
Less than six inches might in insufficient for removal of some deep rooted grasses. The depth need be sufficient to clear anything that might have a tendency to grow other than what you have planted.
One thing you must decide is whether you want two handles that are disconnected, or a bar connecting the side handles. Think about a wheelbarrow, and how you grasp the handles. The hands are at right angles to how they would be orientated pushing a crossbar. Which is more comfortable? Also to be considered is that the separated handles do not have to be at the same height when making a turn, which might make turning easier. So think about how often you will make a turn.
Another consideration is the availability of electricity. Think whether a long extension cord will reach from the nearest outlet. If not, or if you are careless and might run over the cord, cordless models are available, albeit with fewer choices.
Find tillers at K-mart.