When to buy airfare - SEA to MCO

Going to Orlando with my son (8) in August - currently looking at airfare from SEA > MCO on August 19 - 25. When is the best time to buy for this kind of a trip? Prices last week were about $350/ticket for favorable departure times, but now are up to about $465. Any point in waiting due to limited flights, or should I just buy now so that prices won't continue to go up? I haven't traveled in quite some time and I am trying to research, but not really sure what to do in this case.

Any help is appreciated!

Check out this article from USA Today:
http://traveltips.usatoday.com/airlines-discount-fares-lowest-56973.html

This website will show you a monthy calendar of fares:
https://matrix.itasoftware.com/ (Matrix Airfare Search).
They don't sell tickets.
.

Booking with Southwest gives you the ability to rebook if lower fares arise. We have done this many times. Plus, there are no baggage fees. We love traveling with Southwest.

Dori