I used to make them for my Maine coon kitty, they sent him home with a bow and he was embarrassed so I did a bandana. I've seen them selling for 5-10.
the ones I did for my kitty had elastic where you would tie them, so that would mean more money.
Will you be doing them like Rainy said.
Just serging them maybe sell them for $4 each. don't forget..thread, elastic, electricity your time.
see if the 4-5 dollar range will give you enough of a profit and still keep them coming back for more.