Well... shelves and storage are about your biggest expense. I don't have many shelves in mine yet, but the
SmartHome site has prices on all the shelf and storage options.
As far fans, I have 2 fans just like
this one. They are loud, but move alot of air, both above and below the fan module. It's quite cool. I just added a dimmer control to them so they aren't running full blast all the time.
As for other finish out... I have about $30 in mounting and finish out parts (as seen in my pics). That includes some 2x4's, and the trim I used.