I'm thinking the same way - although my use of knowledge gained may not be of actual use, for many a year. Is there a free online guide to the basics? At the moment, I often can't even make my phone's GPS work. I'd like a bit of twisty brass in a wooden box, instead...
I am also intersted although I think that by the time I done the maths that big tanker in the Thorn Channel might well have run me down. So, not much use in my current sailing but am intrested to learn what its all about.
With this http://tinyurl.com/andkub2 you don't even have to buy a sextant. Haven't tried it, but at less than three quid it can't be bad (iphone or iPad)
Plenty of online help with the calculations, but you may need someone to actually show you how to get the best out of a sextant in practical terms.
Most of the cadets I have to suffer with onboard can struggle with the calculations using a calculator, but the majority cannot actually take a sight, mainly due to lack of practice.
For a good calculator and planner have a look at this site