If you join the payless rewards program, you get 5% off your rental ( same as AAA, AARP, etc). There is a Southwest Rapid Rewards code, SWP060, that will get you an additional 10% off and you can use both your rewards discount and the Southwest discount on the same rental.
Payless is a low cost rental car company and there are some disadvantages to using them. But, if cost is your main concern, this method will save you 15% off an already discount rental car company.
I have a rental for 4 days in Las Vegas ( 10/30 - 11/3), economy car for $78, including everything.
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