We haven't bought yet - but I'm watching closely - prices normally come down in a week or so for flying in Sept. Though if, in March, we'd known we were going we'd have purchased (our flights would have been $2000 for 4). In the past we've purchased at around 80 days out and found the lowest prices - so we'lls ee.
Oh and I buy through expedia - always cheaper than direct, even with sales.
The flights actually really haven't gone up in cost in the past 10 years. 10 years ago I paid $700 per person, now I pay between $400 and $650 per person (including taxes and fees). However the fees have gone up considerably. The biggest thing is to know when to purchase - often the farther out you purchase, the higher the cost - except for the occasional sweet deal. However even those sweet deals turn into less than desirable b/c they switch flights around so instead of having perfect times, you end up on the red-eye!

I've spent a lot of time negotiating to get decent times back after they switch my flight - I will not pay more to keep the time I originally booked.
Oh and you're best bet is to avoid Toronto (and other Canadian cities) do customs in Edmonton for the best travel experience.