Here's a lineup of all the types of spike I have. I've been offering these as add-ons to the dragon tails I make, though I'm also thinking about using them in leather projects (which would be more what they're originally intended for). In the background is my own dragon tail for size reference.

For most of these I'll list the price that they would cost to add in to a tail. (For the cone spikes it's tricky because the time it takes to attach them is more significant than the price for the spike itself.)

From left to right, we have:
cone spike size 4, short
cone spike size 13, 1/2"
cone spike size 28, 1"
small dragon claw ($2 each)
large dragon claw ($3 each)
small cat claw ($2)
large cat claw ($2.50)
XL cat claw 1 3/4" ($9)
giant cat claw 2 5/8" ($11)
thin ghost claw ($4.50)
thick ghost claw ($4.50)
giant tree spike size 45, 1 3/4" ($2 for this one, in raw aluminum)
giant tree spike size 70, 2 3/4" ($2.50 for this one, in raw aluminum)

The most common of these for me to use are the small and large dragon claws. They look really good running down the spine of a tail.

Most of these are plated with nickel in a mirror finish. A few of these have other finishes available (like gold or black).

There are more sizes and styles that I can get, these are just the ones that I've acquired because they seemed most relevant or entertaining to me. I get these from studsandspikes.com if you're curious.