You've got to be kidding? Even if someone answered this question, this is the wrong place to request costs like this. contact one of you local storage tank suppliers. They will be glad to give you a budget price, but be prepared to supply additional information so they can supply a reliable budget price.
Thanks MJ Cronin, at least I have some idea on cost.
FTank, I was not trying to get a quote, just a ball park figure on the steel tank. The reason is that the existing tank will need an entirely new floor.