Here is one you can build for you floor jack probably for less than $100, maybe for nothing depending on what you have laying around your shop.
Sorry, it's from a Chevy board
scroll down to post 6
door dolly - The 1947 - Present Chevrolet & GMC Truck Message Board Network
Found the one from our Own Board, It is by MP&C the post was on the metal meet forum http://www.metalmeet.com/forum/showp...&postcount=559