We are getting married on December 3rd. We basically talked to the travel agent and said ... when is the least expensive time for our guests (we were torn b/w May and Nov/Dec b/c those are the best months with my occupation) and she said DEFINITELY the first two weeks of December b/c everyone either flies for T-giving or Christmas and hardly anything in between. So we booked for December.
We chose Dreams Punta Cana Resort & Spa b/c it is kid-friendly and we have 45 kids (yes, 45!!) on our guest list of 215 (I am Irish Catholic and he is Greek = very large families!). It was also reasonably priced for our guests. Many couples that booked in June paid $2,100 for 6 nights/7days. Of that amount, $900 was total for airfare ($450 each person). So $2,100 less $900 = $1,200/6 nights = $200.
The deals have been going up and down and I actually recently found $1,600 for 5 nights/6 days but that quickly passed since it is back up to $2,000. I found that AAA (primarily East Coast company) and Costco were the least expensive. Our TA is through AAA (guests do not need a membership to book through them).
Good luck on your wedding plans and congrats on the engagement!!!