also, it is true things can book up and be more expensive but this is not always the case...especially for a DW...in mexico they do not raise the rates for the long weekend/holidays, instead it depends on the season.
also, our flights were not more expensive BUT they had to be booked earlier and there was a smaller chance they would go on sale....but we stayed for a week so we kind of missed that crunch but we had friends down for 3-4 days and they said it wasnt that bad price wise, they thought it would have been worse.
ps. this is for weekends like memorial day, 4th of july...obviously x-mas and thanksgiving are not great choices to have a DW.