First off I only use Mac BIAB and Garageband so I can't compare it to Real Band.
But since you are using a MacBook you should have access to Garageband
as a part of iLife if you using OSX. Or did your OS come without it?
If you are concerned about hard drive space, my Garageband takes 238MB of space on my HD on a MacBook osx 10.5.8 and 185MB on my Cube with osx 10.4.11