For us, Expedia is the best. In late September, about $3200 (US) for 8 nights, good flights and insurance. Only $300-400 more than three or four years ago.
We used hotelscombined.com and that showed us prices from several sites. Prestigia ended up being the cheapest for us. I also recommend checking allinclusiveoutlet.com
Can't find a deal, go on a referral and pay flights separately. Interjet.com has amazing prices depending on where you live. You will also get all the membership perks as well. PM me for details
I got mine from a travel agent. All included 7 nights, straight flight Montreal Cancun, 2700 CAN$ tax included with premium seat for my long legs.