If you don't have any issues with setting up shop 19 kilometres away from the city's core, look into the suburb of Miyanoshita. It has 3 available options, including Fujiya Hotel and Musashino Bekkan.
For more options, checkout the Gora Tensui and the Furuya Ryokan. They are located 17 kilometres and 30 kilometres respectively from the main center. Further alternatives are the Mikawaya Ryokan, 18 kilometres away, and the Yamagaso, 20 kilometres.
The close by cities of Otemachi and Numazu are definitely worth seeing. Otemachi is 30 kilometres to the south of Oyama, while Numazu is 30 kilometres to the south. Hotels in Otemachi include the Numazu Riverside Hotel and Hotel Miwa. Numazu options include the Hotel Massimo Mishima and Dormy Inn Mishima Natural Hot Spring.
Why not spend a few hours rubbing shoulders and cheering along with Shizuoka sports fans at a local match? Odawara Arena is found to the east of Oyama. The Hotel Kunimi Odawara and the Hotel Kunimi Kamonomiya are close to all the action.
Hotels in Oyama start at AU$141 per night. Prices and availability subject to change. Additional terms may apply.