I got my 4 rolls of 18 inch shrink wrap from eBay over the summer. The price has since gone up a lot now so it is available for about 42$ for 4 2500ft rolls.
Paraffin or Kerosene lamps work pretty well for a small setup as they can add 5-10F of temperature to my greenhouse, which would translate into even more for your small set up. As far as fuel, it cost around 10$ per gallon of high quality lamp oil, but the kerosene is much cheaper, and should cost no more than a dollar a night for operating a lamp.
You could also get one of these portable space heaters, but the risk with these is if you have an electrical outage, these things won't function.
220V 100W Mini Portable Personal Ceramic Space Heater Electric Air Fan Warmer | eBay
A cold winter is not that likely if we are expecting an El Nino along with the northern ice caps being at their lowest in recorded history.