If you plan the job right, you could probably rent one and save alot of money.
What are you going to use it for after the house is done?
Are using this to get off the loose paint or to wash off vinyl siding? If you are using this on vinyl siding, wash with the overlaps of the seams so the water can't get under them and tear off the siding.
Stage the house and start from the top and work your way down.