[ddouglass]

MP3+G is a compression format for storing karaoke files on your computer. It actually is two files. The MP3 is the music (just like you would use for your audio only files). The second file is a the graphics for the lyrics and has a .CDG extension.
The songs are not cheaper and most of the people with this type have converted them from their discs to store back-ups and use them with the computer. A lot of the other karaoke programs out there have used this format for a long time. MTU developed their own format using a modified WMA format which also is a compression format and in my opinion is a better format for sound quality.
I hate to say it and I may be wrong but I have my doubts about just how legal some of those huge numbers of song files are. There are some who have been in this business for a long time and may have collected that many, but there are just too many KJ's out there who share there music with groups of people. One buys a CD and suddenly they all have it.
You can buy songs on the internet for downloading and usually those are zipped up MP3+G to make them smaller for downloading. However most do not have license from the producers to provide those files. I personally would not trust buying from anyone except direct from the individual producers themselves.
Where to get them legitimately I couldn't tell you because I don't even venture into that. Everything I use comes from legally purchased CDG discs.