Osaka to Akita transportation

I was wondering what the most efficient and affordable way to travel would be between Osaka and Akita prefecture. I know that the train (or bus, plane for that matter) ride will be long, but I'm wondering what would be the smartest way to get there, and around how long/how much it would take.

Right now I've looked into flights, which don't seem plausible... and shinkansen - more plausible but expensive. Is there some sort of night train of the sort that I could take for some part of the journey that would be practical?

Air:
3.5 hours from city center to city center, about 30,000 Yen one way.

Train:
8 hours, 27,000 Yen one way

Bus:
No direct bus. But there is an overnight bus from Osaka to Yamagata (12 hours, 12,000 Yen one way). From Yamagata to Akita it is a 4-5 hour train ride (3500 Yen by local trains).

Ferry:
There is a ferry from Tsuruga to Akita that takes 20 hours and costs 6200 to 8000 Yen in the cheapest class (varies by season). Tsuruga can be reached in 80 minutes (4700 Yen) from Osaka by limited express train.

Why is the airplane not plausible?

Sorry about the plane comment, that was a misunderstanding on my part. Thanks as always for your prompt replies Uji! Turns out I won't be going there anytime soon anymore, as it was a bit tight to fit around my schedule. I will look into all the options later though when I have the time to travel up there.