Climbing Fuji from Osaka?

I'm going to go climb Mt. Fuji, but I live in Osaka...what's the best (and by best, I mean cheapest) way to get there? As it stands, we're planning to take a night bus to Tokyo and then take the train to Fuji. Is there a cheaper option? Thanks! :)

Osaka-Tokyo bus is cheapest.
If you start climbing from 5th station of Kawaguchiko side, you'd better take train from Tokyo to Shinjuku station and then take Fujikyu Highway bus from Shinjuku station.(OW JYE2600)to 5th station of Kwaguchiko side.
If you will start from kawaguchiko side, and end at Fujinomiya side, then you can buy Fujikyu Tokyo-Fuji round trip ticket JYE at JYE6000 RT.

There is a direct overnight bus between Osaka and Kawaguchiko Station.

Osaka Umeda 21:45 -- 8:04 Kawaguchiko
Price: 8,500 yen
http://www.yamanashibus.com/kousoku_osaka.htm

Then check the bus timetable to the 5th Station.
http://www.jnto.org.sg/news/47_1.pdf

Thank you so much! Very helpful. :)