Thanks guys. That's exactly what I was thinking,
John.
It wouldn't be as attractive or sturdy, and cost the same, if not more. I was a fully set up 18x18x24 at my show (plants, background, etc) for 160$. Also they had a 12x12x18 zoomed for 125$ fully set up. I was thinking of getting one, if my budget allowed it. I wouldn't be worried about the cost of silicone, though. I know where to buy a 10 oz tube of aquarium silicone for 5 bucks.
Johnny
Arcylic is even more expensive. To make an 18x18x24 it would cost maybe 200-250$! I do think that if I were to ever want to make a custom tank or a large one acrylic is the way to go though.