Putting an explicit monetary value on your time has the advantage of ironing out certain irrational habits. (Of course, if taken too far it could be a source of stress, for example if you were to constantly interrupt your leisure time with thoughts of how much it's costing you.) Here's some advice for putting a ballpark dollar value on your time...
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Up until a couple of years ago I was a complete slob with my time, zombie-ing out in front of the television most nights watching sports, Nat Geo re-runs, and who knows what. I think a big part of what got me away from that lifestyle was thinking of my time as valuable. If we conservatively say that an hour of your time is worth $18, then even ignoring the opportunity cost, a 3.5 hour football game costs you $63 (not to mention the cable bill). I am too cheap for that. I now try to use my time on things, like blogging, where the benefits are compounding and not limited to myself.