From our evolving ZLab3d FAQ page late July 2014:
The most expensive is the resin, but B9Creations castable Red and Cherry resins are much less costly than competing resins.
Next is the clear silicone layer, PDMS, that coats the bottom of the vat.
You’ll also need less cost items like isopropyl alcohol, mixing cups and stirrers for the PDMS liquid, and other disposables for clean up, and storage containers for your finished prints.