Just read the small print on my contract:
"In the event of the retail price being increased the Purchaser agrees to pay the seller the amount of the addition or additions to such retail price, unless, within 14 days after receipt of such notice, he give notice to the Seller that he declines to do so, in which case the Seller shall have the option, by notice in writing to the Purchaser, to cancel this contract, and the deposit shall be returned to the Purchaser."
So there ya go!