I had a PC thread recently about an r10 Tactics -2/-2 Ornate Buckler. I got some interesting replies. You might be able to garner some info from it, as I would guess the Round Shield skin is about the same popularity level. So then the r12 from r10 difference is roughly the only difference.
Here is the
link. NOTE - That thread is now closed. PLEASE do not post new replies on it.
I haven't sold it, so I can't say what it's actual price is, sorry.
Cheers & GL