Eneto,
We don't have a separate meter on the barn's mini-splits. Our house is all electric except fuel oil heat and a wood stove. We bought 4 cords of wood last spring before the prices went way up. We burn a lot of wood and are using a lot less fuel oil than in the past. To be clear the furnace and the wood stove are in the house, not in the barn.
In the barn we have two separate heat pumps / mini-splits, one for each side. That way when when of us is using their half we're not paying to boost the heat on the other side, which we leave set to 50. If I'm out there for only an hour or so, I don't turn the heat up. The mini-splits are also air conditioners, but I only use that once or twice during the summer. We only wanted the heat, but when we bought it there was only heat and a/c.
We also have a solar tracker and a big battery backup, which is another reason it's hard to calculate how much it costs to heat the barn. The battery backup is useful as we get a number of power outages here in Vermont. No going out in a blizzard to start a generator.
Pete