Assuming that you are on friendly or at least cordial terms with the owner, then why don't you actually have a chat with him. What has changed? How many other stock holders are there? Is he planning a big change in structure, investors? Is your stock holding simply a book keeping inconvenience?

In any negotiations, you first need to gather your facts. Once you have the facts, you might be in a position to ask for more, etc.

BTW if by your calculations it has taken 5 years for your stake to grow in value to $3200, then perhaps you could counter with a sell bid of $9500?