I think that the best way to find the cheapest flights is to sign up at one of the websites specialized in airfare deals alerts. However I think you can buy the cheapest tickets for autumn - but it also depends when you buy them..
the cheap time
about February =)
spring break
The cheapest time of the year to fly to El salvador is from February to March and then again in May, and then from August to October.
October
when the kids are at school
during Ausgust or October
March
The cheapest time to go would probably be August, September because it is winter in Australia.
ALL YEAR LONG
i was just wondering the same thing!
The winter off peak season