We stayed here last October ~
we also hired a car for 3 days (which was cheaper cos we booked it on a sunday) but it was 60 euros.
We found the island expensive in many ways, but we used our hire car to get to the sand dunes (cos you can drive down its easier) we parked down the road between the two Riu hotels and it was great location for the beach, and ice cream, toilets etc)
We also drove right the way down to the bottom of the island ~ took a detour on the way but its simple enough. But, yes not the cheapest of places to hire a car, we hired it from the main street (there's a petrol garage a little road and then its right on that corner by the garage) they seemed one of the most reasonable