hi Sniperzele,
welcome to the forums.
rates depend always on what you expect.
of course during x-mas season all is expensive because all is booked anyways.
to book PC for this year's 2008 x-mas week is for sure not too early, the oppiste, i could name you a dozend+ spots which are booked for 2008 x-mas since a long while.
$1.500.- per month for a appartment is a usual rate for short term rentals, mostly in addition to that you have to pay a deposit and mostly you get electricity bill/cable TV/water/maintenance aso billed separately, check those details when getting/requested a offer, otherwise a spot can get much more expensive than the expected $1.500.- per month.
a good reliable address i recommended often with til today always great feedback, but also booked far ahead usually would be Robert Hill from "Apartamentos Mar Tropical" in the middle of bavaro, beautifulbeach access, nice appartments of all sizes.
you can check availability and rates and what's included/excluded with him directly on
rob-hill123@hotmail.com or drop him a call on 1-809-850-6610
good luck
and have a great time on the island
Mike