I learned how to make bow ties when I figured out that they can be made cheaply with very simple materials. Here is a list of things that you will need to make your own bow ties:
A piece of fabric (100% cotton is best)
A Fat Quarter will be enough, 18'' by 20''
A size template for dimensions and measurements
This will save you time and ensure your bow ties are the right size, since it is hard to judge size on the fly, which I learned the hard way. This one here is cut from thin particle-board backing from some old shelves. It measures 5.5cm by 11cm, but you may want to go bigger or smaller. A good way to start is to get measurements from a pre-made one, which is what I did here.
I am using upholstery thread for extra strength, but any thread will do.
Large brass safety pin
I am using a brass safety pin here, but any 2-inch safety pin works. (Brass is just stronger.)
Fold the fabric up as shown. Use your template to get the correct width.