The cheapest version will be almost exclusively midi. They aren't anywhere near as good as the audio realtracks but they are perfectly fine to jam along with at home.
If you're like me, you'll eventually want the real tracks. I now have the UltraPlusPak.
Two things to consider:
Every year for maybe the last 5 years PG Music has a sale during the Christmas season and the discount the prices.
I originally bought the Pro and a bit later upgraded to the UltraPlusPak. That was a less expensive path than buying the UltraPlusPak first.
Today, Pro $129, upgrade from 2011 to UltraPlusPak 2012 $269, $129 + $269 = $398. Todays price of UltraPlusPak $469. Check it out here:
PG Music - Band-in-a-Box for Windows - All Packages
So if you can't wait until the Christmas season, just buy the Pro today and consider upgrading to the UltraPlusPak during the Christmas season discount when they introduce the 2013 version.