I've lived and worked in Belize for about the last 4 years on and off, so I know the place quite well - so I'd highly recommend staying at Iguana Junction. It's a gorgeous spot on the river just on the edge of the village, and you'll be well looked after by the very friendly owners Colin and Dawn, who are from the UK. Its well under 100US a night over christmas and they normally have a deal on at that time of year as well. Brilliant gardens, loads of hammocks to relax in, funky cabanas and close to San Ignacio. Oh, and great home cooking! It would be a stunning spot to spend christmas!
I have been to Parrots Nest and didn't really think it was very nice - quite rundown, dirty and not well looked after and really odd owners - not welcoming at all! And expensive for what it was. Crystal Paradise isn't great either - not a patch on Iguana Junction.
Hope you have a good christmas!