Great advice doobie!  I've managed to get my hands on some great soil amendments that were outdated or damaged.  
Don't get me wrong Bad at user names, I'm on a budget and cheap as hell.  I used miracle grow organic soil on my first grow and it was a fucking nightmare.  I had splinters in my hands every time I tended to the plants and the soil has nothing but nitrogen in it the last time I checked the labels.  For the same price range or a tad more I'd go with the black gold organics mix.  They use peat instead of bark fines and come packed with worm castings already.  It's actually a great bargain base soil to start with, but you have to add everything else yourself.
Here's the trick, invest heavy in the beginning with a superior potting soil and amendments.  That way you already have a diverse supply of goodies in your soil when you go to re-use it, and I do highly suggest re-using it.  That way you don't have to buy more soil and have a banging mix off the bat.  You can do things on a budget, but don't half ass it.