Why do you all want to buy something to help do doors, surely a peice of timber 6" x 2" with a notch cut say 40mm wide and 60mm deep out so the door sits in it and cut a wedge to fit between the door and the notch you just cut. This will clam the door and make a firm place to cut hinges or door lock.
Total cost should 5/8 of FA leaving the money to spend on some more Festool gear.