I know a way to make them, knowing I've made my own pair before =3 However... it's kind of bootleg, they don't go over your ears, but it's extreemely affordable ^-^
What I did was I bought model magic, shaped them into an elf ear form, and then shape the base of the ear to the curve of a plastic wide headband and let it air-dry for 24 hours. Then depending on what color you used (I've used both white and a peach colored), paint it to match your skin color... and let it dry again :P Then glue the ears onto the headband and bada-bing... bootleg ears! The only thing that stinks with this, though, is that the headband has to go in front of your actual ears... and it really hurts after a while. Sometimes if you use a headband where they have a plastic cover over the tips of the bottom of the headband, it won't hurt as bad.
If you want an example of a finished result, here's my Saria costume with the homeade ears - http://images.cosplay.com/showphoto.php?photo=700788
I hope this works for you ^_^!