Lisbon is the capital city of Portugal and if you are looking for cheap car hire in Portugal, Lisbon will be the most  high-priced place to get that. Being the capital city, it is  very  clear that you will get expensive deals here, however if you will have required information and resources earlier you can easily get a bit cheap car hire in Portugal, especially at Lisbon airport. While most tourist arrive Lisbon through its airport, it is quite  understandable that this is where you must know to how to opt for cheap car rental companies.Some of the car rental companies that you can find at check in desk or in the  neighborhood of Lisbon airport are Auto Jardim, Avis, Alamo, Budget, Europcar, Sixt, Hertz, etc. These are the  noteworthy rental companies, where you can find competitive rates and large variety of offers to select cheap car hire in Portugal.
First, since they  propose variety of car types and options; select according to your budget and if unnecessary don’t indulge you in luxury range of vehicles. Of course, select comfortable and spacious vehicle that will accommodate number of members  necessary to travel together.
Next, look around the offer they are providing you. For example, some car rental agencies will  incorporate VAT, insurance option, theft protection, unlimited miles of travel, safety options, etc. You should  bear in mind that for cheap car hire in Portugal, you should have your own travel insurance. Moreover, you should take only whatever services perfectly necessary for you because extra services will come with extra  fee. But since you are traveling through Lisbon, where traffic is very busy, you should try to take minimum safety options and insurance or protection options.
You should also look for some discount offers that these car hire companies put forth together with airliners. For example, with TAP Air Portugal there may be some  partnership with car rental companies that will give you discount as TAP Air Portugal passenger. Just clarify these things before booking your car and you will see that you are getting comparatively cheap car hire in Portugal.
There also are loyalty card schemes, where if you subscribe to these schemes you can get benefits like cheap rentals, discounted offers, fast booking, fast check-in, extra offers, etc. This is particularly very  advantageous if you are traveling  habitually to Portugal and you will end up saving  vast amount through cheap car hire in Portugal.
Lastly, you should also remember that you should carry valid travel  credentials and credit cards as they are  essential to book car hires at Lisbon airport. Sometimes you will be  blessed enough to find with a particular kind of credit cards you can get offers with huge discounts.