Heatherbikes, without pics it's hard to be definite, but judging by your story it sounds like you'll be wasting time and money trying to fix this bike. Low-end Gitanes are not rare and you should be able to find one in better shape than this one (rusty BB / cranks ... NOT a good sign!). Then again, mixtes are harder to find, so why not post a few pics anyway. You might also try the gitane.usa site; those guys really know their Gitanes!

Joseph