Living in Riverside, California, you could watch for fares from the following airports:
ONT - Ontario
PSP - Palm Springs
LAX - Los Angeles International
LGB - Long Beach Municipal
SNA - John Wayne Orange County
BUR - Bob Hope Burbank
CLD - Carlsbad-Palomar
SAN - San Diego International
If you were flying at Christmas break, spring break, or other popular vacation times, I would recommend jumping on a decent fare as soon as possible. However, September is a slow month for tourism in Orlando (and most other places), so airline routes that primarily serve tourists are likely to offer good airfares as airlines struggle to fill seats.
That said, it's sometimes better to grab a relatively good fare when you see one -- especially if that fare involves a convenient airport and flight times -- than to try to save another $50, only to see the price go up $500 as flights fill up.