I've been to NYC twice in December. 5 years ago, we stayed in New Jersey at a Candlewood Suites and we walked to the PATH train. We payed in the 200's for a room, but did not have to pay to park. It was a last minute weekend stay close to Christmas, so $200 was the cheapest I could find.
Last year, we went the week after Thanksgiving, I was able to get a really great price at Skyline Hotel ($150) and they have discounted parking on site. We actually paid less there than if we stayed in NJ. The rooms were nice and clean. There was nothing wrong with the area. The walk to the subway isn't too bad (unless you're carrying a 2 and 4 year old). We were able to walk from the hotel to Rockefeller Center to see the tree. Unfortunately we were unable to get anywhere near the tree the night they had the tree lighting ceremony. I'd really recommend Skyline.
We've stayed several other places throughout the years, each year a different place has worked out to be the best price. From my experience, December in NYC will be pricy, you may not be able to find anywhere cheaper than $200 a night and most will cost a lot more. Also, the rooms can sometimes be pretty small. Skyline's and Candlewood both have decent sized rooms.
Another thing to factor in is transportation. If you are driving in, you will have to pay to park somewhere. Some hotels provide parking for a fee (some are pretty hefty). If you are taking a Greyhound or train, then you should consider a location that is very convenient to Port Authority, Grand Central Station or a subway stop. Lugging your luggage in NYC can get tiresome.
That said, my favorite time to visit NYC is at Christmas time. The decorations are magical. Make sure you, check out the window displays (my favorites are always Macy's and Tiffany's).