I've used Skyauction frequently. Inventory changes all the time and rates can change too. Since the dates you need include a holiday weekend, it is hard to know if the prices will come down. If they have lots of availability, then prices should get lower.
If you are bidding on an auction per night, then the surcharge amount should be added each night. If you are bidding on an auction for a week, then only one surcharge should apply. I don't bid on auctions that have surcharges.
I bid on their certificates for weekly condo stays but have a hard time finding availability holiday weeks or during busy times. The certificates currently cost $239.99 for a week stay. I check availability on Resortcerts.com frequently, do research ahead of time so when I see a good unit / resort I am ready to reserve it fast before someone else does.