On our recent 3 and half day trip, we used Amigo autos, (goldcar), from Alicante, €18 for the whole hire inc insurance, we had to pay for a full tank fo fuel but get back money for any we didn't use.
We were up and down to Murcia a few times and we manged to use 3/4 of a tank.
But we always use them and they are normally unbeatable.
J