Unless you're not planning to fly Alaska any time soon (or you're getting an incredible points redemption for this flight) you may want to pay for this flight and then use the points on your next flight. Other than doing the single (or double) transfer via Marriott you can also always buy points on the Alaska web site but it's not a good value. If you want to buy 1,000 Alaska miles you can do so for $29.56 ($27.50 for the miles + $2.06 tax recovery fee).