Can you tell us more about your speakers? You simply said "monitor speakers", so are we to assume Harbeth, Yamaha NS-11s,or Radio Shack?
If you are going to keep your current speakers, they will probably dictate what integrated amp you need more than our off-the-cuff recommendations.
If your speakers are moderately efficient and like the tube sound, I would not worry about the size of your room too much. A good tube or hybrid integrrated amp might work very well - just make sure that you can try before buying.
If it turns out that your speakers are tube-friendly, you might look at the Jolida line of hybrid int. amps. Folks that have them rave about them. I have had short listening sessions with several models and I think that they are a lot of sonic bang for the buck. No integrated phono stage, but their prices are very reaonable and you might well be able to put together a new system within your budget. Less for used,of course.