I guess that depends on how much you value the hole digging cost. If youæ±*e comparing against a several hundred dollar rental or a chiropractor bill after you dig it probably a year or 2. If youæ±*e comparing against the $30 a month heç—´ paying it would be the length of the payment period.
Well in my case I set a cost limit of around $6K. That was the pain threshold of buying versus renting. As said, if I can get one that cheap than it's there and ready to use anytime I need it. I still have some trees to clear, downspouts I want to run underground to get away from the pole building and house, water line from well, and propane line from tank to house. Plus all the other jobs once I get moved down there. I'll be paying cash so it really is just a matter of how much is it worth to me. Of course then there is the fun factor of having a back hoe just find things to do with it.