Comments about Air Canada and WestJet
Though not a charter in particular at this time of year, if you buy air only with Air Canada, it is stipulated that anybody flying from the DR must buy the return ticket as well. You don't mention that part of the equation and your needs. I suppose you needn't use it if you don't want it, but you may run into that difficulty and have to pay twice the price you'd like to pay if your friend was only looking for a one way flight.
My flight to the DR for last week cost $1000 return when I bought it in March, going from my city to Montreal and to PUJ from there. Had I booked in April the price would've been $700 (both prices include all taxes and extras). Of course that hurt, but I was okay with it since I was inflexible on dates and was happy to be able to have a ticket even for $1000. Without the connector that I had to add on, you could expect a price of $200 less. If booking from the DR means you pay extra, you may end up paying the same rates as I do.
I flew from YUL to PUJ on a Saturday and had scheduled my return for Sunday, a week later. Air Canada changed my itinerary weeks before my travel saying that they'd cancelled the PUJ - YUL flight on Sundays and directed me through Toronto. When checking in at the airport on Sunday morning, there was a window accepting those on the Montreal flight 90 minutes later. I don't know what that was about.
I notice that both WestJet and Air Canada announce their Wednesday sales mentioning international reductions, but that doesn't mean all of their destinations. They are currently offering their sales until the end of September. It may not benefit you to wait if you are interested in that time period. If you are interested in a flight after October 1, you may want to take your chances on an announced seat sale in a few weeks.
Kaki