I checked from the UK Avis site and got quotes for the 1st week in December for between £100 and £150 for the week. ($160 - $240) so roughly comparable.
Portuguese car hire is in a mess. You will get a cheap quote on line and when you actually pick up the car you will find all kinds of extras.
Insurance - If you don't pay for their expensive insurance you are likely to find that you are charged for some minor damage that you didn't notice when you collected the car. You can claim it back if you are insured elsewhere but it is a hassle to get the necessary documentation.
Deposit - They will put a charge on your CC for €1000 to €2000 depending on the company and the car. Any extra costs like damage or tolls will be charged to the card with no explanation.
Fuel - The most common arrangement is for them to charge you for a full tank, regardless of whether you will need that much fuel and how much is in the tank when you return.
Edited: 8:00 am, November 20, 2012