Where I really started shaving off the cost of my materials is when I found Bricklink. You can go on there and find legos that are less than $.01 (a penny!!!). So we just stayed with the basic 2×2 lego brick in cool colors for this school project. To be really creative, you could build colors together, use different shapes.
This was a project we were supposed to do together. My daughter could help with some, but not all of the assembly. I did not want her dealing with the epoxy, so I did that myself. I also cut the ball chain in 16″ links, and I had to affix the fastener (she tried, but could not). My daughter did thread the lego onto the chain. She was so proud when we took the necklaces in to school.
Things I considered when getting my materials together:
1. You have to get a bail that has an opening big enough for the ball chain and one where the flat part has enough surface area to hold the glue and affix to the lego itself. I think the best is one big enough to also reach the middle of the back of the lego so you have that surface area contact.
2. I found these cute paw bails that were cuter for kids than the fancier, more expensive classic looking bail.
3. I thought Home Depot would have the ball chain and fasteners cheaper, but they did not even carry them in bulk like Ace did. I bet you can even find that stuff cheaper somewhere.