If this is is your only journey, then it's not worth to buy a pass. You can check fares on www.raileurope.com and compare with pass prices (+ reservations).

Local tickets are still very expensive-they go with advance sales on the superfast AVE.
Note that the seniors from 60 y can buy for 6€ a year-long Tarjeta Dorada=f=gives 25 or 40% OFF all RENFE-fares for a year-can be bought on the spot. But mostly you need that Tarjeta-nr to make a cheaper booking.

IF you fancy also other long-dist RENFE rides, then RENFE also offers its own online pass-good for 8 trips in 1 month-all online and without any exyra fees.

NOTE that-ONLY if you ask this when buying, the AVE tix alsominclude a local ride on cercanias trains-even at both ends, so you could erach Torremolinos-Fuengirola out of MLG with that