I think celestial navigation to get absolute position is not that useful for backpackers. (Of course it's nice to find north using the Big Dipper, and stuff like that). But even with a decent marine sextant, sight reduction tables, and a precise chronometer, the best position fix you can expect will be plus or minus several miles. That's accurate enough to steer across the ocean without going way off course, but not much help finding your way back to camp in the woods.

Much more useful are coastal navigation methods. Rather than sighting on distant astronomical objects, you use your sextant to sight on known landmarks like mountains and measure the angles between them, and then just use a protractor and ruler to find your location on a chart. A sextant is probably too bulky for backpacking, but fancy backpacking compasses have gun-sights for measuring angles like that, albeit with less accuracy than you could get with a sextant.

Finding position at sea was the great navigational problem of the early seafaring era. The British Admiralty offered a huge reward for a practical method in the 1600's, and many fancy astronomers tried to invent purely celestial techniques and failed. Only the development of the accurate marine chronometer (which most people back then thought was technologically impossible) made a practical solution. Dava Sobel's book "Longitude" tells the story and is fascinating. There was a PBS video made from it, which you might be able to find at the library or something.

Bowditch's book is downloadable for free (the US government bought the copyright from the author in the 1800's and has been updating the book since then) so paying $60 for a CD-ROM sounds like a rip-off to me.

Here's a real cool page someone here found recently, about how to make a sextant from a CD-ROM and case:

http://www.tecepe.com.br/nav/CDSextantProject.htm