I must admit that Don's website is not all that user friendly...

I found the tach on the "Accessories" page just a little way down from the top of that page on the right side, but couldn't come up with a direct link having the pricing information.

I usually call them...

Or you can order the tach direct from Fromeco, that's where mine came from;

http://www.fromeco.org/atnc_tach.htm