I have been making my own for quite some time. Once you get the hang of it - it isn't too hard. I still buy some when they are on sale. Do you have the fuse system? Wondering what their largest plate measures.
I haven't used cereal boxes, but I've made them with 3 or 4 thicknesses of cardstock, cut with the same exact pattern and glued together. A bit time consuming but custom! So cool! I've only made smaller ones cause I have a standard Big Shot, but the same techniques apply.
I use chip board, cereal boxes, whatever I can get my hands on, then cut a pattern on my Pazzle machine and glue them to the opposite sides of thick card stock that is folded to make the folder. I learned the technique from a video on you tube it works pretty well as long as you aren't doing extremely detailed patterns. I just bought some thick plastic and have not tried cutting it yet, hopefully within the next month I will get to that project. I also do some embossing with my Pazzle machine but not everyone can use it at the same time on club night and a 12 x 12 page takes a while so the folders work out better.