My husband and I just got back from our honeymoon in Belize and had a fantastic time at the La Milpa Biological Station in the Rio Bravo Conservation Area.
Beautiful place, amazing birding, nice accomodations and good food. Plus the staff were incredibly friendly. A lot of our guided tours were just the two of us and the guide. We went on night hikes, toured deserted ruins, and saw at least 50 different species of birds. All the guiding was included in the price of accomodation. Best of all the profits all go to support the reserve.
We were in Belize for 16 days and had a lot of great times but this was the high point of our trip. And it was so much cheaper than Chan Chich Lodge, the nearby "luxury" lodge that all the tour guides recommend.
Here's the website for La Milpa. You may need to be persistent in confirming your reservation but believe me it's well worth it. http://www.pfbelize.org/lamilpa.html