I move your question to the transportation forum.
If you are able to introduce city name in Japanese, you can use this site to calculate the price with ETC.
Trip price calculator using ETC
The ETC is quite tricky, close to Osaka and close to Tokyo you will not have the reduction and even during week-end you will have to pay more than the 1000 yen.
The company taking care of ETC is NEXCO, the highway company. It is worst to register to their website as you will also have point every time you use ETC and you can use this point for reduction ticket (only in Japanese). You can also have nearly 50% discount if you drive between certain hours, mostly after midnight.
NEXCO - trip cost
Look at this map and I try if no mistake to explain
Map of highway
Violet > need to pay, no reduction
Yellow > need to pay, no reduction, inside town
Green > no reduction, proximity of big town (Tokyo, Osaka)
Blue > 1000 yen available during week-end
Red > no fee highway, they do it to increase traffic on those road
Hope this will help, don't hesitate to question more if necessary