I need to heat a 640cu.ft. uninsulated shed that is outside without spending too much on a heater or e.bills?

YOU'LL BE WASTING MONEY FROM THE START TRYING TO HEAT AN UNINSULATED SHED. INSULATION ISN'T THAT EXPENSIVE, PUT IT IN AND SEAL IT UP WITH SOME DRYWALL. YOU'LL SPEND THE MONEY ON HEAT WITHOUT IT. TAKE THE MEASUREMENTS OF THE INTERIOR TO H.D. AND THEY WILL TELL YOU WHAT YOU NEED AND HOW MUCH IT WILL COST. USE CAUTION WHEN CHOOSING A HEAT SOURCE. DO YOUR RESEARCH AND ASK LOTS OF QUESTIONS... GOOD LUCK!