Depends on the ground, if its easy digging, a back-hoe medium size ($75/hr) could probably do this in a half hour....but, they need float time to get the machine to you and back. Are you installing the tank yourself? If not its probably best to get prices on the whole job, it would be cheaper, otherwise, you will need to dig the hole, have the tank installers come, do their thing then call for the machine to come back and back-fill around the tank.