How much is a blue diamond worth?

Answer 1

That depends so much on the diamond. You cannot ask a question like that without giving the specs on the diamond first. What is the carat weight? What is the clarity? cut? etc. Without that information, I could say $.50 or $5,000,000.

Answer 2

More details are needed. The 4 C's. Cut, Clarity, Color, Carat.
The setting, if any. 14K or 24K? Silver? Platinum? Ring or bracelet? Pendant or necklace?
True blue diamonds, not treated are rare, so they are usually expensive, but you could have a poor quality stone that isn't even gem quality, just mineral quality. Give more details and ask again.