I want to know how many calories I am actually burning, to that end I need a fitness tracker that tracks my heart rate and does the math for me.
I don't need anything that does text messages, email, alarms, weather, GPS, anything like that.
What's the cheapest most accurate way to do this?
Garmin lets you set your calories per day, which you can get measured at certained locations (RMR: resting metabolic rate). Garmin instinct is a great tracker, and if you're looking for something a bit more fancy, the Fenix is a great series, too.
Edit: I can't find the settings for setting daily calorie burn, but my calorie tracking does line up with my RMR pretty well.