We also go to Costco often. They seriously mark down any toy (and other items that are not regularly carried) that is returned. This year, we found $50 sets of Playmobil for $20 and a large Star Wars Lego set for just $10! We also found an illusion set that one daughter really wanted, but by the time she had saved enough for it, it was gone. One was returned and was only $9! She was so happy when we brought it home. Last year we were super-blessed to get the $120 set of Playmobil for $12!
Watch the clearance shelves especially after Christmas, and then again in the fall as stores prepare for Christmas. You may be able to get special things for much less!