One option is an older Gravely walk behind. I used a really old model when I was a kid (my dad had bought it used when he was in high school). My uncle has a "newer" electric start model. Do a search to see what I'm talking about.
http://cgi.ebay.com/Gravely-Walk-Beh...item2eb5872ca0
They have a bush hog attachment on them and you can put dual wheels and such on them. They are super reliable.