If you're strictly using it as an hlt and not mashing in it, the insulation properties of a cooler aren't as necessary. Certainly nice, from a heating efficiency point of view. Given that you've got the temp sensor, I presume that you've got a pid or some such to keep the water at desired temp. From your location I'm guessing that you're not brewing in the snow, so fighting to keep your water heated probably isn't too much of a battle.
I suspect an economy kettle would serve your needs. Adding reflectix to the outside would be easy if you want to stay electric, or you have the option to use a flame to do some of the heating if you prefer.