If you're doing it in relatively small areas you can make one fairly inexpensively with a 3' length of 2x4 really whatever size you want), bolt a piece of angle iron lengthwise on the bottom, then drill a couple holes on the ends and put a loot of rope for your hands. You can then step it down the row you're working. Not gonna go through acres I'm sure, but you could make it through a decent sized garden lot fairly quickly