Several Lego sets are on sale at Costco, online and/or in store.
LEGO Ninjago The Crystal King $49.97 online, $54.99 in my local store [$79.99 at Lego.com ]
LEGO 71403 Super Mario Adventures with Peach Starter Course $30 in my local store [$59.99 at Lego.com]
LEGO 66712 Monster Jam™ Collection, LEGO® Technic, $50 ($59.99-$10) in store [No LEGO official price, but each car is about $17-$18 ]
YMMV, please check with your local Costco store.