The rates quoted on line are for basic hire and
you pay for any damage up to the excess. The hire companies will not quote on line for full cover - you get that on arrival.
Once you arrive to pick up the car, you will be asked to take out super collision damage waiver, Super-CDW. I've holidayed in Portugal for the past few years and Super CDW there costs approx €15/day = €210, depending on the model/class.
Last year I got an annual policy for europe to cover it. Cost €80!! Try this link:
http://www.insurance4carhire.com/index.asp?curID=2&refID=553&pID=47&langID=1
Think twice before you decide to forego the cover. For the past year or two in particular, car hire firms have been hitting people hard for damage to wheels, windscreen, paint etc. You will be charged up to €1500 for any damage, irrespective of whose fault it is! The other guy may be 200% at fault but you will still be charged - and you will already have agreed to this on the hire form.
Inspect the car before you drive off from the pick-up and detail any marks/damage and have the rep counter sign. Ideally take photographs of any damage. It will take a few minutes.
btw, the hire firm were NOT pleased at all when I pointed out that I had the multi-trip insurance - very frosty response.
Finally before you hire, check out if you have any possible discounts available, e.g. professional bodies often have arrangements with the hire cos. Discounts can be quite sizeable.