Depends upon whether or not the OW ticket is non-refundable or not--most tickets priced well below "market" are non-refundable. And the airlines mean just that. Ya pays ya money. Ya takes your chances. Be aware that the closer you get to the date of the trip, the price tends to go up--especially on one-way fares. Waiting until the last minute to book will mean the fare OW or RT will be very expensive compared to an advance purchase fare. But you are looking at almost a year in advance. Quite frankly, I didn't know any airline allowed bookings that far in advance.
Considering how slowly Puerto Rico is recovering from the hurricane, do you really want to book a ticket now? If your purpose is a vacation, do you know that your intended hotel will even be in operation yet? Were you to buy a non-refundable ticket and ended up with no place to stay, the airline would not be inclined to refund your money. The hotels and the Puerto Rico infrastructure are not the airline's problem.