Thanks for all the answers first.
Now 170 yen is still cheaper than here, as it is 200yen in switzerland and around 250 yen in Germany and France.
To Nyororin: Well i plan to move around the rest of the time. I want to do a travel for about 2 Months in Hokkaido and than slowly move back to Tokyo for Winter and work there. After that i wanted to move south. The actual plan was to use camping as cheap alternative to Hotels and maybe spend some nights just on the roadside (outside the citys off course!)
Well im not a lawbraker, the only thing i ever got was 5 parking tickets abd 1 speeding ticket for 1km/h to much.... We also got a point system running in Germany and i think thats more than good. I was just curios if i can risk driving 60 when there is 50 allowed or will i face a fine like in Switzerland for that (that will cost you more than 100$ there!).
Well about the 250 a day, i was aware that i will be driving all day for that, but i have time and i will maybe be a bit faster around the rural areas (like most of Hokkaido). If i go this fast i can cover 2500 in 10 days and 5000 in 20. So lets extend that and say i´ll do 10000km that year, so i spend around 40 days driving, wich i think is alright, i probably spend more in Australia on Highways, but Australia is bigger.
To MMM: Well my plan was to move around alot, as i also like to see some spots off the beaten track and they are mostly hard to reach on public transport. 2. i can carry all my stuff without worriyng, wich can be pretty anoyinng if you dont have a car. I can transport a small gas-oven and i can buy food and dont have to throw it away the next day because i just cant carry it. 3. You can stop anytime and anywhere when you see 4. more of the scenery between the citys than in a train, bus etc. You can maybe find a travelmate or invite people on a weekend trip.
I know using the car inside the citys is crazy and i will try to avoid it like i did in Australia. I checked in, in a cheap place on the outskirts of the city where the had a parking and than always went to the city by bus or train. Worked out pretty well.
Note that i will take a little bit more money with me than most people on a WHV, so i hope that this will somehow work out. If not, than thats also ok, but first i want to try that out.
A little calculation. Lets say i do the 10000kms in the year and lets say petrol goes around 180yen all year round. Now lets say my car takes 10l for 100km than i would run a 180000 yen wich is around 1800$. I dont know how much i might spend on trains and busses to cover that distance AND come to the special spot you hardly reach without a car.
Now why buying i can could rent? Ever calculated how much a rental car costs for lets say 4 months? I can easily get 2 cars for that price.
Thanks to everyone anyway