That has been discussed before. In comparison with very high end, all carbon, long straight boards as now being used in the F18 fleet, the curved boards aren't THAT much more, perhaps a few hundred per board.

Price for long boards: http://www.reverie.ltd.uk/product_list.php?group=M%20FOIL

Long board=$1300/board, last F20c foil price I heard was ~$1800/board. Both prices are likely wrong and subject to change.