SXM was approximately $120 per litre as of my visit on 12/24. I also thought $16 for 2x 1 litre bottles of Stoli was a nice buy. The new terminal is very nice, incidently.
Total OT: I was very disappointed with the prices of havana cigars at SXM. They are a complete rip-off (over 2x "la cas del habana" in SBH) and the duty free shop didn't seem to have very good humidity control.