You can get discount tickets from www.ticketmania.com and AAA, as well as a few other discounters.

Don't count on the discount being more than a few dollars.

As well, the expiring tickets do so after 14 days (perhaps 10) of initial use, so it's not likely anyone will have any lying around.

The expiring tickets never expire - as do single day tickets and can be traded in for a longer ticket at any park, so I doubt you'll find anyone interested in a trade