Please excuse the terrible quality of the photograph and the apocalyptic mess of a desk on which my feet are propped, and focus on the sandals:

I made these from a kit from
InvisibleShoe.com, who will sell you a sheet of 4mm Vibram Cherry rubber and a pair of nylon laces, and provide the instructions on their website.
I modified said instructions slightly: I decided that rubber against bare skin was going to be unpleasant in the heat and used Shoe Goo to attach a layer of denim from my rag bag, leaving it rough around the edges (because I like the look and because I'm lazy), and I pulled a loop of lace through the toe hole rather than a single strand so I could modify the tying system and make them simpler to take on and off.
I'm really pleased with how they've turned out. It's taken a few days of wear for the lump of the knot under the sole to flatten out, and for me to learn how to wear them (mysteriously, it's easier to walk with them laced more loosely), but they're now very comfy and I expect them to be my standard wear when it's too hot for shoes.
If you're in a climate which is sandal-friendly at any point in the year, this could be a good cheap way of trying out barefoot shoes and seeing how they work for you.