Hi, there are buses that run every half an hour or so past Club La Costa, the resort itself is in between 2 bus stops on the main road, easiest option to get to Marbella is walk down the road to the BP station (3 min walk on the main road), there is a bus stop there.

The bus you need is the number 220.

Coming back, there is a bus stop on the opposite side of the road to the BP station, just use the footbridge to get back to Club La Costa.

They are supposed to run on the hour and the half hour, but are sometimes 5mins later or so depending on traffic and time of year, summer is a busy time and if the buses are full they don't even stop, but in October you should be fine

Hope that helps!

Steve