It depends a lot on HOW you travel, and how far. If you use shinkansen (bullet trains) the costs add up quickly. The trade off for the $ (or whatever currency you are using) is the speed of travel. If you have time, slower trains are cheaper.
To figure out costs, try the following site to look at trips you KNOW you are going to make in that 2 weeks. You should be able to decide if the railpass is a good deal or not.
Enter the station name
best,
................john