Honestly, when I played, (trying to resist the urge to start up on the money pit again) I just used paints from Michaels too, and my army looked great. The only problem I ever had was with metal minis, and that is just because I hated priming the figures, and I hated painting on metal.
Gah now you have me wanting to play again, though I got rid of my army. I was thinking of starting up a Tau army (mainly Kroot) or Space Marines again, or Tyranid, or ....yea...see my problem? I really wanna get into War Machine too...ahh different time different place.
Anyway, 40K is a lot of fun. I wouldn't drop all the money for GW paints though. Inks are nice. Once you master the whole dry-brushing and inking things, you will be golden.