What I did on my mule:

Level monk naked solo to lvl ~12.
Run to Gusgen mines.
Join a book burn party and stay there until level 30.
Run to jeuno and start the Dancer quest.
Follow the guide on the dancer quest to obtain it without having to spend any gil.
Level dancer solo naked to level ~12.
Run to Gusgen mines.
Join a book burn party to reach level 25+.
Congratulations, you now have sneak and incis and didn't need a single gil for it. You also have enough conquest points for reraise scrolls, and enough tabs for reraise, warps and Circumspection WHICH IS AVAILABLE IN AREAS WITH THE HIGH LEVEL MOBS THAT YOU SPEAK OF AND GIVES YOU SNEAK AND INVIS!

If you're really keen, take your dancer to crawler's nest and reach level 55 to get Chocobo Jig for increased movement speed when you are able to use circumspection.

That is all, enjoy.