Link to prices and options:
http://www.sonycreativesoftware.com/vegassoftware
The cheaper versions are basically the higher end programs with fewer features.
Have used Vegas for around 9 years and have been very happy with it.
Same here (Studio Pro).
My son has one of the lower-end Vegas programs with a few add-ons, and he’s been happy with it, except he has a crappy laptop and it takes forever to process his stuff.
I’m about to get an I-5 processor to see if it will speed him up.