AI am making cake pop bouquets as centerpieces for a wedding. The vases the bride wants to use are taller than we originally discussed. I need opinions on what I can use for filler. Since I'm going to need a lot of filler I want it to be cheap. All the vases have been spray painted so I don't need to worry about the filler being pretty. Since there is food involved I don't want to use sand. I was thinking rice might be the cheapest option but I'm open to other ideas. Thanks.

floral foam.  It will keep the cake pops in place and can be cut to fit any vase shape.

Floral foam from the Dollar Store, and put shredded paper around the top to hide the foam.  If the foam doesn't stay in place, put wadded up tissue paper around the sides to make everything stable.