This is from the
Budget site:
Will my credit/debit card be charged when I make the reservation?
Answer: No, unless you choose to prepay for your rental at time of reservation.
Regardless of whether or not you prepay, your card will have a hold placed on it at the time of pickup. Please check the terms and conditions on your reservation confirmation or the location information page for the dollar amount required at your desired location. And while it's perfectly fine if you choose not to return the car on or before your scheduled return date (see "May I extend my rental beyond the original return date?"), we’ll place up to three additional holds on your credit card (depending on how long you keep the car) to cover expected rental charges. Upon your return of the car, all holds will be released, and the actual cost of the rental will be charged. Please note that your bank may take up to two weeks to post the released credit hold to your card. Unfortunately, we cannot be held responsible for any returned checks due to credit hold processing. Important related information may also be found under the question "What kinds of credentials will I need to present when I pick up my rental?".
http://www.budget.com/budgetWeb/html/en/customer/commonquestions/index.html#Will my credit/debit card be charged when I make the reservation?