Continuing the DIY theme, there are many other easy to make yoga props. Wooden blocks are a good one to start with because they can often be had for free. Take a trip to your local lumber yard and check out the cut-ends and scraps. There will often be pieces that are the perfect size for blocks, or that you can easily ask to have cut to the perfect size. (There really is no "perfect" size, but anything 2.5"x5"x9" or bigger will work.) A little sanding to smooth any roughness, and voila, your handmade set of blocks. Bonnie's desert blocks are a perfect example.
Along with blocks, straps are probably the most used prop in yoga. Sophie has experimented with various material and closure combinations. The yellow strap is tubular nylon with ladderlock, the blue strap is nylon webbing with ladderlock, and the black strap is also nylon webbing with snap release. Sophie doesn't recommend the webbing - it's hard on your hands. The tubular nylon is nice and soft. It would probably work well with D rings. Everything is bartacked for stitching, and the ends seared to prevent unravelling. A good online source for strap material and clasps is Textile Outfitters
There is nothing quite like an eyebag to take your savasana up a notch. Choose a fabric that will feel nice against your skin, like smooth silk or velvet. Cut two pieces no smaller than 4"x8" and sew them together with a .5" seam leaving one short end open to put in the filling. Flax seeds are the most popular filling, and if you don't mind scent, it's nice to add some dried lavender blossoms. Rice and lentils also work. Don't stuff the bag too full, you want the filling material to be fluid.
Another simple "fill a bag" project is a sandbag. A sandbag adds a gentle weight to your body that can help with release and relaxation. Sophie's sandbags have an inner bag of very tightly woven nylon to keep the sand from leaking out. But since that's slippery when you use it, she also made an outer cover of cotton. They close with snap tape. Fill the bag with about 5lbs of clean sand (aquarium sand is nice and clean). A handle can be added to make them easier to move. Again, it is important that the sand have room to move within the bag.
Zafus and zabutons are associated with meditation and are also useful in yogasana. There are already good online instructions for making these yourself:
Make your own zafu and zabuton
Make your own zafu or seiza bench
Instructions for a simple meditation cushion