I wasn't going to answer this as I replied to a similar question asked by you about 2 weeks ago. However, having read what "jackie m" has said, I felt I should.
I'm going during the first week in October (4th) as I do every year. The weather is usually lovely (mid 20's), the sea IS still warm enough to swim in and the majority of attractions are still open, albeit on restricted hours. The water parks, Parque Acuatico Mijas & Aqualand, Torremolinos will be closed and Tivoli World Theme Park is open weekends only but this is to be expected with the children back at school. October is, after all, not so much a month for families and, indeed, many people like to take a holiday when there are fewer children about.
You'll have a great time on the Costa del Sol and at half the price you'd pay for a holiday in Tenerife.
My week is costing around £208 for flights and hotel on a half board basis. I've used the same hotel for a few years now, usually 3 times a year, and it is well recommended. In addition, you will find that the Costa del Sol (unless you choose Marbella/Puerto Banus) is very reasonable to drink & eat out, if that's what you choose, and buses and trains are cheap & frequent.
So, yes, the Costa del Sol is a VERY nice place to go in October.