There's one tunnel in Europe that charges roughly £35,000 per day and has a minimum hire period of 3 days. Ouch!
On the plus side though you can test 20-50 different configurations in a day in a wind tunnel and be fairly sure of what is good/bad, whereas on track you've got to have a good driver and consistent wind/track conditions.
Something i find strange, however, is that many people go into the wind tunnel and are happy to just try stuff they've conceived themselves rather than get a professional aerodynamicist to advise them. It's kind of like going to an engine tuner's and asking him to read the paper while you have a fiddle yourself. Odd.
