John is quite correct as usual. In the past I have been buying only certain genre's of real tracks such as jazz, bossa, etc. since I don't do any country stuff. However, I think you will get a better deal if you just buy everything. To me it really depends on how much you use the software also to justify the additional costs.
Another thing with real band.....You can make/use a midi track and record it to audio. You can then merge all the audio tracks to a single .wav file. In other words, you are not just limited to using a single melody and soloist track as you are in BIAB--at least that's what I've been doing. YMMV
Find the Real Band intro video and you will see just a few of it's capabilities. When I first got it, I didn't pay much attention to it, but thanks to the nice folks on this forum, I find I'm using it a lot now.
Stan