YYZ to SDQ or LRM !!!
It will take a great deal of patience, but you can do it.
If you are flexible you can find selloffs, (
www.selloffvacations.com) but you must sit down and search every day. For example you can go to La Romana air only this week for 209.00 +tax, there were tickets yesterday to Pto. Pta, for 189.00+ tax. My husband bought a ticket once for 99.00+ tax CDN$
In my experience the time frame you want to GO is great for cheap flights,, there is no much activity as the kids just went back to school a week before your scheduled date. I have gone to LRM and drove to SD and saved over 300 CDN$. You can always buy two tickets,,,again if you are flexible,,,use the return portion to come back.
You can drive to Buffalo and flight with AA to San Juan connecting with American Eagle and also save,,,that is a bit more complicated,,, long, long, long time to get to the DR,,, but it all depends on your budget and the kind of sacrifices you are willing to make in order to save.
I was in the DR for 8 months in 2003 and I bought 1 year ticket with Continental for under 900.00 CDN$. Either way,,, you have to do some homework.
CB