Sakhalin media reports that, in President Vladimir Putin's meeting in Vladivostok one subject was a fixed connection from mainland to Sakhalin and to Japan. There are big projects. The cost of a fixed line from mainland to Sakhalin is estimated 600 billion rubles. According to Governor of the Sakhalin Region Valery Limarenko, it is not whether these connections will be built. The question is when it will be built. He says whether 10 or 20 years, whether a tunnel or bridge, they will be built. Bridge is more mentioned between mainland and Sakhalin and a tunnel between Sakhalin and Japan. 

https://sakhalinmedia.ru/news/1203854/?from=41/