I found this out and feel like it is my duty to share the word with everyone. I found this at Life in Rehab. I guess it should be common sense that mod podge is just glue and water, but I never would have had the guts to try it myself first.
It works great! Costs like 50 cents. I made it for a favor for a craft day I hosted along with a foam paint brush. It was a nice touch.
I'm probably going to reference this post a lot since I have already done so much with it.
So go ahead, give it a try. Let us know what you created with your super cheap homemade mod podge!