Last Day Is TODAY 5/31: Renew Costco membership now to avoid price increase in June 1st, 2017: online 3mos in advance, instore 5mos in advance.
Update: so far you can update 3mos in advance online but 5mos instore up to November due date.
I just paid $110 at my local warehouse.
It didn't even show on screen my membership due date late next month yet but I asked them if I can pay for it now or not and they rang the old price of $110. I did honestly told them I expected to pay $120 due to price increase in June 1st and the lady called the manager to clarify. He told me that's OK if I pay now with old fee, the system will ring in the new price on June 1st. I'm a little greedy asked him if I can pay like few years in advance my membership fee and he said it won't allow it, only 1 year at the time.
So if you want to save few bucks you can ask to pay your membership fee now at your warehouse. I don't know how far it can go, my due date is June 23rd.