So the ticket was $5830, which means only $330 in taxes / fees, which somehow seems reasonable to me. (I had expected 10% or $550).
I don't have the breakdown though, and don't know how it might have been different w/other code-sharing options.
I took the AA codeshare both to CBR, and on the way back on from NRT to JFK (wasn't available DCN to NRT).
best,
Shawn