I wouldn't personally by an aquarium with any crack no matter the price. The money you save will evaporate pretty fast if that tank springs a leak and does damage to the stand, flooring, and stock!
Unless you are planning on replacing the cracked glass and resealing the tank -- but for me personally, that would be too much trouble.
The money saved isn't worth the risk in my opinion.
"I wish, I wish, I wish I were a fish" --Henry Limpet