You have some golden advice given here. I make a living digging with a backhoe and an excavator and these people are spot on.
If your digging is so infrequent to not warrant an excavator/backhoe then consider renting an excavator/backhoe when you need one.
For $20k id find the nicest backhoe that I could. More versatile than an excavator. An excavator will generally out dig the backhoe pound for pound but you can't haul/spoils any distance with the excavator like you can with a backhoe.
If your digging is so infrequent to not warrant an excavator/backhoe then consider renting an excavator/backhoe when you need one.
For $20k id find the nicest backhoe that I could. More versatile than an excavator. An excavator will generally out dig the backhoe pound for pound but you can't haul/spoils any distance with the excavator like you can with a backhoe.