PeterS,
The only reference I could find regarding the Cd of dustbin fairings suggested it would be around .44. Using this figure, together with the known bhp, frontal area, weight and performance, seems to agree quite closely with the calculator.
Don't be afraid to make you own fairing, it's not rocket science. I found a photo of the one that I made but never used. Basic shape made out of chickenwire, then covered with fibreglass, there are plenty of instructions on the web. It wasn't as lumpy as it looks in the photo, the plan was to smooth it out with body filler.
Get yourself a donor and make a start, it doesn't have to be finished in weekend. In the worse case scenario you can put it back to standard and sell it on. Take a look at Craig Vetter's build, Chapter 47 (I think), there's a photo of David Hyatt with his recumbent Honda passport.
Ironside