Second hand tanks are not worth much by comparison to new stuff - obviously they are used, they don't have a warranty, and you don't know its history. If it really is a metre tall, you might have difficulty getting enough light penetration to grow certain things in there, and pumps don't last forever. I would expect to pay around 25-30% of the new price, assuming everything is in good working order. If it cost $2000 new, that's about $500-600 max.