I'm a karaoke addict. I used to go there every weekend by myself or with friends, and each session, solo or group, would often range between 6 hours to 10 hours at a time. My longest record of solo-karaoke is 9 hours, from the moment the shop opened to it closing. Having been to most of the karaoke chains in the country, there's one that I always go back to.
Ban Ban karaoke tops of my chart of karaoke chains. Its extremely reasonable price is unbeatable. I went there with friends recently, and on a weekday, free time (we sang from 11am to 8pm) and drink bar included, we paid about 500yen per person with the help of the 20% coupon that's often in the local coupon magazines. The drink bar in also included, so there's no one-drink requirement BS.
Granted, the ones I go to are in the suburbans. It would cost more if you're in the city, and Ban Ban is rarely in the center of the city. But Ban Ban is indeed nation-wide, and their machines are very updated too. If I have access to a Ban Ban, I rarely visit others. Look up if you have a Ban Ban near you!
How often do you go to karaoke, and do you have a favourite chain?