How do I measure the cost of mistakes ?

[Rotating Rabbit]

Putting a $/hour rate on your play is, I think, only a bad thing for your head to mess with you. Its past performance , and does not mean you can repeat it. If the world worked this way we could look at a financial share-graph for a company and predict its future based on that. As others have said its better to concentrate one hand at a time, each hand is statistically (maybe not psychologically) independent from the next.

I think having a benchmark in your head while you're playing is a very risky thing, because the moment you exceed it you'll get complacent or afraid to lose it, and when you underperform you're running a risk of going on tilt.