How much do you think a tattoo like this would run me?

That's a very detailed piece, unless you plan on doing it on your shoulder, back, or possibly upper arm (depending on how large your arms are), no one will do that on your lower arm. Are you wanting it on your wrist? It's not a good design choice as a small tattoo. Even if you want the circle to wrap around the forearm, it's not a good design choice. It wouldn't flow well with the body, it would look very out of place. If you do that too small, it will look like crap in a very short time.