What is the approximate cost range (wholesale) for GOOD 3-carat
samples of the following jewels:
diamonds, sapphires, emeralds, rubies, pearls.

What is a good website that can provide further valuation questions
(other than blue nile)?

It might help to be more specific as to what you mean by "good."   For
most gemstones small differences in quality mean very large difference
in price.

Let's replace 'good' with 'near flawless'.  I'd also accept an answer
that said the RANGE of prices of a 3-carat sapphire, etc... is X (poor
quality) to Y (flawless)

- the philosopher

Dear Friend
I am engaged in gemstone and diamond business and would like to help you.
Could you please more specific?Please mention the clarity,cut for
diamond and exact color of sapphire ,emeralds and rubies.Only then one
can be able to answer your question precisely.
With best regards,
Pradhuman Jain