I'm renting from L&M for this trip because I needed an in airport agency because of my flight times. They were the cheaped at 286 compared to alamo at 425 (for 8 days). If you don't need something in the aiport try enterprise or U-save. I've rented from both and had fairly good service with both. Both offer shuttles from the airport to the agency, but they close around 11 pm.
L&M gets both good and really bad reviews. You must show proof that your insurance includes rental cars (ie. the paragraph on the policy that states it, not just an insurance card). And I've heard of them raising the price when you go to check in. I'm hoping if I bring the confirmation email they sent that I will be ok. Oh yeah they also have policies on using cash and debit cards.
CASH:
3 day minimum rental
Minimum Age 21
It is L & M policy for cash rentals that the renter must purchase additional coverage (SLI and CDW)
$500.00 deposit over the rental is required
Must present a return airline ticket to home state at the time of rental.
The rental agreement must be the length of travel.
No specialty cars
If you rent the car it is a $20 per day fee, if your 22 yr old friend does it is only $15.
Check out the websites
L&M Car Rental
Enterprise Rent-A-Car
U Save
When are you going? I'll be back May 24, so I can let you know how it goes as an underage renter, with a credit card, proof of insurance and my email confirmation.