Mega Bloks Big Building Bag, 80-Piece (Classic) Just $11.19 (Was $24.99) This post may contain affiliate links. Please see the full disclosure policy here. Posted on November 22, 2013 Written by Kristen Dann Leave a Comment Their back! The Mega Bloks big building bag, 80 piece is on sale again for just $11.19! This is an awesome deal and I bought them for my son the last time they were this cheap. It is tons of fun and there are so many things you can build.