The man thinks the price of the necklace is no deal.
What is the meaning of 'no deal' here?
I agree with MikeNewYork. The phrase is often used in haggling. The would-be seller names a price and the potential buyer replies "No deal."
And if the buyer say 'it's no a deal' it probably means 'it's cheaper than usual.'
Am I right?
A deal is when the buyer and seller agree on terms. Once a deal is made, the transaction can go ahead.
Perhaps you mean "It's not a deal" - that's still wrong. For cheaper than usual, you'd say, "That a good deal" - though you wouldn't say it to the seller. You might say to the seller. "That is a fair deal. I'll buy it".
These often used, seemingly simple, words can be applied differently, even in the same exchange.
Buyer: How much is the old bicycle?
Seller: It's $50
Buyer: That's no deal, I can buy one for $40 at the XYZ shop.
Seller: I'll take $45.
Buyer: A/ No deal! I'm going to XYZ shop instead. (No deal = negotiations are finished, we didn't come to an agreement. No sale.)
or B/ Deal! Can you help me get it into my car? (Deal! = negotiations are finished, we came to a satisfactory agreement. Sale completed.)