AWOL:
but maybe this article on Parabolic Microphones could minimize hearing loss
Only $700.
Bargain
Ouch, wrong one, even in a 4 for 1 sale, (why the ...k do I always forget to type DIY in my searches ?) 
Anyway, this one may be affordable, this one certainly is.
GoForSmoke:
Keep in mind that the speed of sound is affected most by temperature then less by humidity and pressure.
Now that you mention it, travelling in air, windspeed should... be... compensated as well.
It's indeed a lot of arduino-ing the arduino, measuring a piece of rope, will probably be simpler to get a 1 inch resolution. (measuring/ rolling it electronically would at least be easy using an arduino).