I am getting $90.14 estimated now! How close to the "estimated price" are you actually charged? And how fast will I get the Costco card in the mail? Do I have to have it in hand to use code? Or will I get some print out from Costco when I purchase the membership? I don't have a Costco anywhere near me, but DD25 has one by her house and the car will actually be in her name with my DH as the 2nd driver (we don't have a Visa).
Estimated price has always been the final price we have paid. We always use the online check-in so never been persuaded to add any extras at the counter to increase the "estimated" price.
If you use the Costco code during your reservation, you will be required to enter your Costco number on the final page of the reservation (just below flight info) before hitting the "Book It" button. If your DD goes and gets the card, she can give you the membership number to make the reservation.
If you/she purchases the membership in a Costco store, the card is issued immediately. If you order it online, you will receive your Costco ID in the email confirmation of the order but you are required to visit one of the stores to get the actual card issued (go to the Member Services counter, it's usually the really short line right next to the crazy long return/exchange line). Cards are issued in the stores because they will take a picture of you and it will be printed on the back of the card (a fraud prevention measure)
And final answer: if you don't have a Visa card to pay for the reservation, then you can't use the Visa $30 off code. If you join United airline's frequent flyer program (Free to join) you can use their $30 off code which is AD2492ACX
FYI: I always find it more convenient to book my reservation on the actual rental car's website (ie: alamo.com, budget.com etc) rather than through a booking engine (priceline, expedia, etc) or
travel agent or site (ie: costcotravel.com etc).
I will quite often use search or booking engines to get an idea of best prices (carrentals.com, carrentalsavers.com etc) but I will use the info I find there and book directly on the car rental website. I don't have any issues with changing or cancelling reservations this way.
One more thing, never book a pre-paid rate unless:
A) it only a day or 2 before you are leaving and it's a great rate or:
B) it's an AMAZING rate, your plans are set in stone, no major catastrophes looming (hurricane etc.).
Pre-paids have a change or cancellation fee so any last minute changes in your plans can negate any savings from the pre-paid rate. Also you will usually (but not always) find that a pre-paid rate has to be changed by calling and speaking to a CSR,
Bottom line with pre-paids is to check what the change/cancellation charges are before booking. My feeling is that if the cancellation fee is about the same as the amount you are saving (by pre-paying) then it's not worth it.
On the other hand, pre-pay can be a way of managing you vacation expenses since you will already have been billed (and presumably paid for the rental) before you leave and you won't be returning home to this bill along with all the other incidentals that you put on the CC.