Have you tried http://hotelscombined.com or http://kayak.com?

Both have great databases for hotel content, but I'm not sure of what restrictions they have for their API.

P.S. I also know Wego (http://wego.com) have an API in the works, if you can get in touch with them through their contact form they can probably work something out (Disclaimer: I used to work at wego.com)