I checked the price of a one day ticket on ticketmania.com and it was more expensive than a one day ticket on the Disney website. I followed both through to the end so that the final price was displayed. Ticketmania was more expensive and you had to pay $7-$12 delivery fee (making it a lot more expensive) or drive to their office to pick it up for free. On Disney you can pick up the tickets at the park gate for free. If you are not planing on having a car or simply don't want to hassle trying to find someplace as an out of towner then buying from Disney is cheaper and much less hassle. Ticketmania over all was more expensive for a one day one park ticket.

Disney one day ticket picking up at park gate $79.88
Ticketmania one day ticket going to their office to pick up $84.98