I suggest making a strong emotional tug to finish the copy. It sounds like you have a product or service that will make them more competitive. So, why not close the letter with something like, 'so the choice is yours, you can continue (describe business or activity) and hope that your competition does the same, or you can take advantage of this limited time, risk free opportunity to get X'. I find that when I am writing for a business owner one of the most productive methods is to offer them a solution to a problem and the opportunity to get it before their competitors.