if you are renting from them they collect you at airport. go to bus terminals level 2. Turn left at exit and go to stands 1 or 2. Mini bus picks up every 10 mins. its only 5mins journey. I came in on Wednesday evening.
When you leave the site just turn right out of gate and go straight on at round about. It takes you back through airport so you can pick up the road you want. It leads you back to the main Murcia road A7