There are 2 types of music on this site: Royalty free music collections (for unlimited repeated use) and non royalty free individual tracks (for one-time licensing).
Royalty free collections are downloadable albums containing 10 or more tracks and are £39.99 for lifetime use of the album.
Individual tracks (non royalty free) are either £9.99 (to license for non-commercial use) or £29.99 (to license for commercial use) and are for use in one video/production. Or you can just buy the music track for personal listening (e.g. on an iPod) without a license for £0.99 each.
More details can be found in the licensing info section.