Kwing is right, Royalty Free Music is like paying someone to take care of all the copyright paperwork and legal actions that tie in with a piece of music. The point of this fee, is to make sure that if you make loads of money on a video/gaming production, the artist for your music, can't come back and try to pocket some of that money you earned. So unless you plan on making money off your productions then go with incomptech or some of the other public domain tracks. Here are some other sites for free tracks:
http://www.smartsound.com/royalty-free-music/youtube/
dig.ccmixter.org/
joshwoodward.com
youtube.com/audiolibrary
betterwithmusic.com
However, if you plan on making money with your productions, GO WITH THE ONE TIME FEE. Trust me, its more of a hassle to deal with copyright if your videos come back tagged and don't have the rights to that track. We are talking not getting paid thousands of dollars for a video production, when it only would have cost you around $50 for the track. Also if you do plan on spending that money, make sure you are reading the fine print for what you are paying for. Most good websites will provide a license agreement that tells you if you are paying for full redistribution purposes/unlimited uses, or if you plan on using the track only once. Anyways good luck and hopefully this helps!