I'm waiting for someone of these guys who tells me I can't use my
handheld GPS to navigate to explain to me how it is that presumably I
can look slightly above my yoke-mounted GPS and look at the stars
(presumably celestial navigation is still an acceptable means to these
folks) and navigate with my sextant (along with my RadioShack
timepiece.)

It's not a direct answer to your question, but if you want a cheap sextant,
check out http://www.tecepe.com.br/nav/. I think an aviation sextant needs
some kind of level, but I am sure this design could be modified. :-)

John Bell
www.cockpitgps.com