I got quoted $125 for an hour. Some places charge for a number of runs.
I'd say it's worth it for finding major bottlenecks in your engine and for getting a baseline. It would also be nice to find out what your exact power curve is so that you know when to shift. I don't think it would be good for making little tweaks here and there on a computer controlled vehicle.
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351W 89 Mustang GT Convertible