Cheap Billiards, Darts, Internet, and more!
Yuyu Kukan is the cheapest place in Hamamatsu to play billiards. It costs 400 yen for the first hour and 100 yen every 15 minutes afterwards. Additionally, there's free drinks (sodas, juice, coffee, and tea) while you're there. They also give 100 yen coupons on request (just ask the front desk), making it cheaper than it already is. You can also find coupons in the Hot Pepper magazine, found all throughout Hamamatsu.
In addition to billiards, you can also play ping pong, electronic darts, browse the Internet, watch DVD movies, read books and mangas, play PS2 games, or even relax in a massage chair! All for the same price and you can change activities at anytime.
I *highly* recommend Yuyu Kukan. You will need to become a member (good at all locations) and pay an initial, one-time membership fee of 350 yen, but it's worth it.