hi, i just built an 800x800x800 cube in 12mm starfire
the costs were approx:
cube - R3200
black silicone - R300
sump (800x600x400 8mm normal clear) - R600
not sure how much the steel for the stand cost but i think it was about R1000 incl some paint
if you want to galvanize the stand then i think (depending on the weight of the stand) you might have to pay about R600
also factor in pricing for some odds and ends when building yourself (paper towels, blades, masking tape, duct tape, etc.) - R300
also, the plumbing can also get expensive depending how you do it, 50mm ball valves cost about R80 each - R800
you're looking at about R7000 give or take
cheers
ant