Don't argue with them over market prices. This is a very simple matter. Correct me if I'm wrong.

• You gave them 90+ BTC for a product.
• They didn't have the product and/or were unable to send it.
• They kept your 90+ BTC.

You are not responsible if they sell your BTC in the meanwhile. They are. No legit business would spend someone's funds before the delivery is fully completed, let alone spend it without even sending the product! Accepting anything less than a full 90+ BTC refund is unacceptable. Also, it's entirely disrespectful of them if they're trying to weasel you around to get free bitcoins from you.