What would be the best/easiest way to measure the amount of power used by my workshop?

I have a standalone woodshop that I work out of. The main panel has a 30amp breaker in it that feeds the subpanel in my shop. Since this is a home business I would like to find a way to measure the amount of power my woodshop uses over the year so that I can deduct the cost on my taxes. What options do I have for doing this? I'm decently comfortable with doing the work myself. I have run electrical runs for several mini-splits and wired the woodshop completely. I also know when to call someone in, but if there is a DIY solution I would like to try that first.