If you've got a tractor you don't need a Mule, IMHO. Last month I made a pickup bed for Mrs WD's 48 volt Club Car golf/garden cart and she drives it all over the place. The cart cost us $2000 with a newish trailer. I made the bed out of some leftover plywood and the angle iron from an old bed frame. This this is super handy and I've got all of $2050 in it. We've got a 23 hp Kubota tractor and between them we can take care of 10 acres easy.
Mr's WDs 48 volt Club Car garden cart, with pickup bed and roof mounted tool carrier.
