Thank you for all the responses. The option I linked has a minimum order of 400', so unless we're all going camping together that's a bit much.
I currently carry two army ponchos in my pack that I have rigged as a rainfly, but I've never been tested on it because the few times I've done it the weather has been good.
I think I'm just going to pickup some 6mm plastic drop cloth at Home Depot today and test it out next weekend on our 2 day hike. I'll let you know how it goes.
There was a thread where a guy made a tarp from Wal-Mart shower curtain liners. That could be something to look in to.
Here is the thread on WV's adventures with this material. He used 2 mil material and Gorilla Tape. This is a some what common practice for people DIYing tarps as it is pretty cheap and can give you a good idea of what the tarp you're planning to make will look like and how it will cover your setup.
Thank you Catavarie. That's what I ended up buying for our 2-day hike next weekend. kayak karl warned me well when he said 6 mil was heavy, too heavy.
Now I'm looking at this:
I made one from a 2 mil plastic sheet. 12×9 cut it hex. Came out ok. Set it up a couple times but hasn't been tested yet
Yep, that's what I'm going to do. Until I make my own.