I found these colorful diecuts at the dollar store. I made all 3 centers out of the same $1 pack. Then I just put it in envelopes I already had and decorated them a little. The most expensive part was probably the Velcro dot I used to hold the envelope shut :)
Obviously, this is not rocket science, but it was fun to make and to share. ABC order was something I otherwise would've done with pen and paper, and trust me the kiddos loved this much more!