Disney's basic pass starts with your choice of a number of days per ticket. For additional fees, you can add park hopping, which allows guests to visit two or more parks each day; water park admissions; and/or non-expiration, which allows guests to use remaining days on their tickets on future visits.
If you don't want to park hop or go to the water parks, you can save yourself a lot of money; but, do consider the potential long-term savings of buying the non-expiration option. For example, if you visit for five days this year and five next, you might pay less overall on a 10-day, non-expiring ticket, rather than two, separate five-day tickets.
For the most part, Disney itself does not typically discount tickets. More often you'll get discounts on package deals as a Disney resort guest. Check the Walt Disney World Website; price out your hotel and tickets separately, to compare the package offerings.
There are discounts available from a handful of authorized ticket resellers. However, buyer beware; look for a Better Business Bureau seal. Seek a physical street location near Disney, to indicate it's an established business. A true reseller also cannot use the Disney name in its name, either. Average savings are only a few dollars per ticket, but those dollars can add up.
Some Disney fans will attend a timeshare presentation to snag cheap or free tickets. While this can be a legitimate practice, consider whether the time and energy spent in a presentation is worth the savings. Some folks say yes; others just want to get to the parks.
Only pay by credit so that you may dispute a sketchy purchase; never buy or accept a used pass. You'll either find the ticket has no days left on it, or the turnstile will deny you entry. Tickets are nontransferable. Disney scans visitors' fingers to "tie" tickets to their original owners.