Ours just went up to $10 per semester. The reason yours is probably $300 per sister is b/c you are a local organization and are only insuring your group of women. A national organization will get a lower rate b/c they are insuring all of the women in all of the chapters. It's very similar to a large company or say the university having health insurance for all of it's employees. They will get a much better rate for their 1000 employees than a small business will for their 25 employees.
Of course with a local group your actions will also dictate if your insurance increases, the draw back of a national group is that even if my chapter doesn't do anything wrong but the chapter at XYZ College does, then the collectives insurance could go up.