I assume you are the owner of the unit since the transfer fee is payable by the seller? Or, if you are a buyer, it is a good question to ask before buying since the financial responsibility will become yours when you sell.
Either way, it is board-specific; you can find out from your board (or the seller's board -- be sure to ask!).
Typically the transfer tax is calculated one of three ways:
Dollar per Share
Percentage of Net Profit