What kind of "good discount" code are you referring to, and what are the details of the rental you wish to make a reservation for? Is the rental pick up and return, or one way? What is the pickup location? Weekday or weekend? Without context, "good discount code" does not have a lot of meaning.

Also, by discount code, do you mean a coupon code, or an AWD number? They are distinct, and can often be used on the same reservations. Unfortunately, some people refer to both coupon codes and AWD numbers as discount codes. Coupon codes have expiration dates and are generally very specific, while AWD numbers usually may be used on every rental, and do not have expiration dates. On Avis.com, there are different fields for entry of each type of number.