The Become A Guardian page explains in detail what you get with each upgrade package. As of June 8, 2009, these are the different upgrade packages.
$34.95 - Guardian Plus X-Boost Upgrade Plus 5000 Z-Tokens
$24.95 - Guardian Plus X-Boost Upgrade
$19.95 - Guardian Upgrade
$19.95 - X-Boost Plus 3,000 Z-Tokens
$ 9.95 - X-Boost Upgrade (can only be applied to existing Guardian characters)
The Z-Tokens page explains in detail the different Z-Token packages.
$49.95 - 20,000 Z-Tokens
$34.95 - 12,000 Z-Tokens
$19.95 - 6,000 Z-Tokens
$ 9.95 - 2,500 Z-Tokens
$ 9.95 - for existing Guardians/DragonLords/StarCaptains/AQW Members
$19.95 - for non-Guardians
Remember, it is a one time payment to become a Guardian! It is not a monthly fee.
Note: If you choose to pay with a payment option where PayPal or PayByCash has to wait for the payment to clear, such as with an echeck, you will be upgraded only after the payment has cleared.