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Sometimes DING! is cheaper, sometimes not. For example, I bought my tickets from Dulles to Disney a few weeks ago for $49 each way. This was bought during a regular websale and I never got a DING for that cheap on those days, so in that case, DING was not cheaper.
Alternatively, in 2007 I got a DING three weeks prior to my kids' Easter break and I got $49 each way. Couldn't get near that price going through the site regularly.