How much does a 20 cents diamond cost?

If by 20 cents you mean .20 carats, you may be able to purchase such a diamond using this example as a guideline.

Today, on Blue Nile, you can purchase a .23 carat diamond and pay between US$270 and US$782, depending on the colour and clarity that you want. A .23 carat diamond is the smallest diamond available for sale at Blue Nile today.