Actually...there are several versions.
If you're willing to sign up for a deputy service(basically, you bid on Yahoo Japan and they obtain the items for you since most Japanese sellers won't send outside of Japan), you can get it for much cheaper. They sell the real deal on YJ, not the crummy SonMay version.
The cheapest to get will probably be the 16 song version because it basically features major theme music from the series. However, there's a larger 5 CD set which features background music, transformation music and some of the theme songs that were only availble during the season's production(ie. Haruka had a theme song for the Sailorstars season). I would suggest getting the 5CD pack..I have it, and I really enjoy it.