I bought a pair of Cats Ears from the US about 5 years ago and I think they were about £12 delivered - now seems a lot more for shipping. (I had the Standard type - that they did in different styles then - Elvis
for me rather than Silver Fox which would be more in keeping.
One of our club members made quite a few sets for the members of a tour - fur fabric and some Velcro strips sewn on (you could probably hot-glue the velcro?) - just wraps around the helmet straps - simples.
They really do work, I wear mine all the time and they reduce wind noise dramatically as well as keeping the ears slightly warmer -and enabling you to hear traffic. Of course the headphone users and no-helmet riders may have a problem ...