Not that it does you any good, but Garage Band makes it pretty easy to score your movie and time everything perfectly to the action/edits. it comes with lots of loops, sound effects, etc. I purchased a USB keyboard that I'm slowly learning to play, so I can compose simple suspense tracks that are timed for my project.
Now, back to something that might help you ... do you have any musician friends? You might find that they are happy to play you a little something for a movie credit. I hate to ask people to do things for me for free, but I know several people who have offered, and one of them is really good. What you need isn't complicated, is just has to set the mood. (You can easily do a normal audio recording from a normal old piano.)
Sorry I can't offer any more suggestions. I'm sure there are web-sites that offer free clips. I'm just not sure if you can find something that is going to be a good fit.