You are right that ballet improves flexibility and balance better than almost any other activity you can think of.  However, done improperly it can stress your body badly.  Ballet uses your muscles in very subtle ways.  Many times, what you think you see, is not what the muscles should really be doing.  For that reason alone, you need a live instructor to show you the proper way to dance.  Perhaps you could arrange private lessons from someone who teaches the local kids if no adult classes exist.  Other options would be a trek to the nearest big city to take class, or sign up for an adult ballet summer camp like the one offered in Richmond Virginia.  They will have 2 week long sessions this summer, June and August.  I went last year and had a ball. I plan to repeat this summer.

Good luck, and feel free to write (you left something out of your e-mail address, because I tried to write you directly and it didn't work).  It's always fun comparing notes with other caught with this affliction!-Scott