I keep my insulated 25'x30' stand alone shop heated to around 65 all the time with a 5000w electric heater without any trouble, but I'm in north central Kentucky. While we hit 0 degrees a few times, it rarely lasts for long. Big difference from Wisconsin. Electric is relatively cheap here, too. Last I read, we were the 8th cheapest state for electric. My heater is ceiling mounted, a 220v unit. The big plus for me being it doesn't take up any floor space like every other heater (propane, wood, & kerosene) that I've used before. It also requires almost no attention & presents no fire hazard.
IMO, it is key to keep my shop constantly heated. I spent years warming my shop up in the evenings & some of my tools really regretted it. They would stay cold, moisture beaded on them & rust attacked. Iron power tool tables are especially vulnerable, but inside other tools, like planer blades with a bit of sawdust on them, also suffered greatly. Dragging in finishes or anything else that can't take freezing is a hassle & I always missed something. Since we're 30 minutes from town, that's an additional pain I don't need.
When we moved here & I built my shop, I planned to keep it heated all year & insulated accordingly. The biggest loss was the top of the insulated garage door. There was a gap across the top I could put my hand into. I bent up some coil stock & attached it to the top to close that up. Worked great. I have no idea what it costs me to heat my shop nor do I really care. I spend a lot of my free time in there, so it's worth it.