This is probably the easiest and cheapest (not to mention the most mess free) way to give hay to your rabbit, guinea pig, or other pet. It's wonderfully quick to make and approximately take 15 - 20 minutes.
Step 1: Step One: Cut Holes
Cut two holes in the fabric as indicated in the image. These holes will be where the hay comes out of and where your pet can access the hay.
Step 2: Step Two: Glue Edges
Glue the two side edges down, but don't glue the top together, or there will be no place to add the hay in! Use hot glue, fabric glue, or sew it. Make sure the wrong side of the fabric is facing up at this point.
Step 3: Step 3: Flip It
When the glue is dry (15 - 20 minutes if you used fabric glue), flip the entire thing inside out, making sure the right side of the fabric is facing up.
Step 4: Step 4: Add Backing & Hang It Up!
Take a sheet of cardboard and cut it so that it fits nicely into the rack. This will ensure it remains sturdy and will prevent it from falling of the wall to wish to hang it off of.
To hang it up on a solid wall, cut two small holes in the back of the hay rack and attach it with hooks. To hang it off of a wire cage wall, cut two small holes in the back and then hang it to the bars with zip-ties.