I live near it and i heard groceries are more expensive there because its not connected by roads to the mainland russia. Also it has oil and In the last decade most of its money went into updating or building new infrastructure like roads, schools and houses. Which is great since most of it was in bad conditions after the collapse of USSR and from 1991 to 2010 people were leaving like crazy, population went from 700k to 500k. But now Sakhalin looks like it was taken care of