You may find that the local immobilario`s provide cheaper than the websites.
I`ve seen the same property in a window and on the net and the deference in price was quite big around 80 euro`s a month more from the net.
You could try http://www.kyero.com
If not just google rentals in Costa del Sol area.
Although 6-9 months isn`t classed as long term rentals, and many landlords increase the price of a rental in June,July and August.
some friends of ours moved out in every August and returned in September as the landlord wanted 800 Euro`s a week for August, the rest of the year he`d struggle to rent out the flat, so they were happy with this arrangement.
Most landlords if you rent through the summer will add the loss from summer trade into your agreement if you rent over that period.
So if you rented from Sept- May it would be cheaper than May to November.
If you rented 12 months you may get it cheaper than 9 months, although with the current property/tourism callapse it may have all changed since we renewed last year.