I don't need too many sounds, just drums, bass and depending on the music either some backing sax/clarinet or banjo/ slide guitar etc. I'm happy to play any lead breaks that are necessary.
If I could convert some of the midi real bands to a decent sound the put them into an MP3 format I would be happy.
THis sounds to me like the MC7 Cakewalk deal would suit the bill perfectly. You get the drums and bass in the Studio INstruments package.
Unless you step up to some of the really high dollar sample libraries..... Think Kontakt and above, AND.... you know how to program the nuances of these particular instruments, you will not be able to get a believable sound from the midi banjo, guitar, or slide guitar.
As good as midi is on some things.... bass and drums, and piano.... it's really not very good on the lower end of the sample/patch scale on other things..... woodwinds, brass, fiddles, and guitars to name a few.
That is where you need to learn how to do audio editing and work with the Real Tracks from Real Band to get what you need. You can actually get the real tracks sounding excellent with a bit of effort editing. The other option is to have a live, talented, player willing to record that track for you.