If you are flying into Orlando during the day, you can stop by the
Disney Store in the airport and purchase your passes. They will be activated at that time - you do not receive vouchers.
If you are driving down, you can purchase activated passes at the Disney place (not a regular store) in Ocala.
You can also purchase passes at Guest Services at Downtown Disney. This can be rather busy at times, but still usually less busy that the ticket windows at the parks.
There are no discounts on the AP, so you don't have to worry about anyone having better pricing.
Usually when you order the passes and they mail you the vouchers, you have to pay shipping.