I just checked Deb Wills site, and both Alamo and national have rental agencies at the Dolphin and the car care center. I know when we were there in 2005, they picked us up from the resort (WL) and took us back after we returned the car.
Not sure about the rate....I booked directly with Alamom (got the phone number fromt he front desk) and was quoted an outrageous figure but them I asked if they had an AAA discount and they said they had a special going on, and I got a great rate! (We were so disheartened with Disney transportation that trip that I would have paid anything for a car! lol) You might try the Alamo website direct. You can also look for discount codes at Mousesavers:
MouseSavers.com - Disney Discount - Disney World Discounts - Disneyland Discounts
I will see what I can find about launch sighting locations!