No experience with COPA, although I was in Panama 25+ years ago and flew Eastern. Orbitz is showing a round trip on Delta (SFO-SXM-SFO) for about $446.45 for travel in September. COPA should be able to come close to that number - depending upon when you are traveling. It's a longer flight, but perhaps you could work out an arrangement for a day or two in Panama as well. It's worth seeing the Canal.