It looks like if you make a purchase on the NW online shopping mall after registering for this promo you will receive a 1000 mile bonus. One of the terms and conditions indicates if you have shopped on the NW mall within the last three years, you will not get the 1000 mile bonus.
So your mission today, is to find the least expensive item from an eligible merchant and pass the info back to us. I did not see a minimum purchase amount to qualify. Keep in mind shipping costs as well.