From Tokyo to Daisetzusan NP (budget)

What is the most budget way to travel from Tokyo to Daisetzusan NP..
This is my schedule as followed:

From Tokyo with JR Tohoku Shinkansen to Hachinohe (3 hours). Then, to Hakodate with JR Hakucho limited express (3 hours) and then the JR Hokuto limited express to Sapporo (3.5 hours).

Another option is to take the night train, but that takes longer (17 hours). Advantage; you don't have to transfer all the time.

I will intend to stay for one night in Sapporo (maybe stay there till noon) and then the train to Asahikawa (80 min). With the bus to Tenninkyo, Asahidake or Sounkyo.. I haven't decided yet.

Follow up questions:
1. Is staying in the Daisetsuzan NP 2 days enough?

2. Is it neccesary to rent a car around that area? Or is it enough to rent a bike?

Thanks :)

What is the most budget way to travel from Tokyo to Daisetzusan NP.

By Air Do from Tokyo to Asahikawa Airport. The earlier you book, the cheaper are the tickets.

Is staying in the Daisetsuzan NP 2 days enough?

Two days in Daisetsuzan National Park is my recommended minimum. But access by public transportation is infrequent, and can be time-consuming. Therefore, if you travel there by airplane, I recommend to allocate a total of at least three days to your entire Hokkaido trip assuming an early departure from Tokyo on day 1 and a late return to Tokyo on day 3. Four days would be better. If you travel there by train, I recommend to allocate at least four days to the entire Hokkaido trip, since the journey to Daisetsuzan NP takes a full day one way; five days would be better.

2. Is it neccesary to rent a car around that area?

No. There are buses. But it is recommended to have private means of transport, such as a car or bike, for more flexibility. It can save you lots of time.

More about car rental in Japan:
http://www.japan-guide.com/e/e2024.html