In the world of royalty free prices can get crazy quick. I will try to answer your question(s) in a couple parts for ease of reading:
There are plenty of places on the net to get free royalty free stuff and depending on your project will determine what is right for you. I can't stop recommending Kevin McLeod and his website: incompetech.com he has huge collections of music for use in just about anything most require only attribution if you don't want to buy royalty, and his prices are crazy good compared to most.
Another route you could go is "public domain" anything created before 1923 is in the public domain so most classical music, hymns, and things like that, but new music can be released to the public domain for anyone to use how they see fit. A simple google search will render thousands of sites with public domain music, video, and images.
-create your own
Well I've gathered your on a budget as most of us are some of the tools I use are things like audacity, since you are on a mac you should have access to garage band if I'm not mistaken? I am a PC guy myself. I don't have much experience with creating music as I'm not a musician, but with today's technology anyone can do it look on youtube for guides or vimeo.
I hope this helps.