It may be easier to go from Algiceras (or better still, Tarifa) to Tanger where insurance is still available at the port. Tanger is probably an easier option as regards border formalities also, and with the new road network is as quick and easy to get out of and toward wherever you are heading. Tetouan is not far from Ceuta but there are regularly Police at every island and junction between the 2. It's also far enough to have an accident and need insurance before you've had chance to buy it.
Tim is about right on the price, however the periods are normally 10 days or 1 month. So if you are there for 2 weeks you'll need a months insurance.
There are 2 offices in the row of shops across from Algiceras Port that claim in their window to do Maroc insurance but I have never found either of them open!
HTH
Ian