If you can find a Garden way era Troybilt, which is an older machine, they are rebuildable and well worth doing it. If you can, try and find one with an 8hp Kohler. It is a brute. Not good for small gardens.
Other real workhorses are BCS(expensive but industrial grade and can take other attachments) and Honda. I was looking at an Ariens tiller at HD and it looked good in your price range, but I don't know about long term survival
Again, parts are available for Honda and BCS and they are rebuildable.
One tiller that crops up every now and then is a Roto Hoe brand. They look like the designer/builder went down to the local hardware store and built it from off the shelf parts. I'd like to try one and they look dead nuts simple to keep running and seem to be build like a russian dumptruck.
I have heard some bad things about the newer Craftsman and MTD based tillers related to them tearing up their transmission parts and replacements being hard to come by.
Look for something with reverse and counter rotating tines if you want to break new ground.
Have you thought about just renting one when you need it?
