Don't use Priceline or Hotwire. If the rental company refuses to give you the car, you will be the one who has to start world war 3. Even if you want the rental collision, it does not make sense to bid $15. a day for a car with $19.95 collision extra (total $35.) rather than reserve directly for $20. a day with $9.95 collision extra (total $30.).
1. If you have neither your own car collision insurance nor a credit card that has the collision benefit, you should either find a short term insurance policy from your insurance agent, or buy the rental company's coverage.
2. Unless the rental company policies say otherwise (find them on Travelocity.com) whether or not you buy the "optional" coverages is up to you, not them. You may repeat calmly as many times as you want that you are declining any coverage you do not want.
Rental companies may tell all kinds of stories to get you to buy insurance. Example: Florida law requires that cars go out with collision (false).
All rental companies I know of say that their collision coverage is not insurance. Experts say it is just a fee for the company's promise not to hold you responsible for collision damage. If you don't need or want that promise, you should not have to pay the fee. Otheriwse that fee is simply a refusal to honor their promised rate, otherwise known as bait and switch, which is illegal in most state.
If push comes to shove, you can tell your own stories at the rental counter. Like, if they won't give you the car, you will rent from some other company and hold them civilly liable for the difference in rate. Here it is advantageous to rent from a nationwide company since then you can go after them after you return home.
In case of difficulty you can also call the rental company headquarters from the pay phone in the rental office using the nationwide 800 number (another advantage of dealing only with nationwide companies).
If you decide to buy insurance or coverage against your will just to avoid the hassle, write the words "under protest" after your initials even if it runs over other printed material on the paper. This will also help if you decide to raise a dispute with the credit card charge after you get back home.
Disney hints:
http://members.aol.com/ajaynejr/disney.htm
If you don't have collision on your own car, the credit card coverage, even if secondary, will pick up with the first dollar of coverage. In some states your personal car's property damage insurance will pay first, then the credit card company's collision benefit. Also the credit card benefit, even if secondary, will pay any deductible.