If you want full-coverage car insurance, I'd go with Seguros Multiples. For a vehicle worth approximately $8k, expect to pay around $750 for the year. They provide 24 hour roadside assistance throughout the island (not sure about Culebra and Vieques).
One caveat: you have to pay it up-front or enter into a debtor-creditor relationship with a third-party company used by SM for monthly payments (I think a 3 or 6 month payment plan is standard - I do not think you can stretch it over the course of the entire year. Besides, the longer the payment plan, the higher the interest.)
Good luck witht the move!