The fundle really reminds me of my "healthy back bags".
You mention stitching one up... if you're pretty good with patterns I've seen patterns for something similar. A couple months ago I was browsing through the books at Joann's and saw a pattern for a tear-drop shaped bag like the
Redefining Style :: Classic Healthy Back BagŪ
I would think it would be pretty easy to convert it into a bag similar to the fundle. In fact... you really might not have to convert anything at all. I tried finding the pattern myself a few weeks ago with no luck - but if you go to a fabric store and just sit down and look through the books you should be able to find it.