Depends on direction of travel. SFO-BKK is currently US$111 for taxes and carrier-imposed surcharges right now. BKK-SFO is US$220 as you say. A round trip is US$251 when originating in the US. A round trip is US$411 when originating at BKK. (This is based off of revenue fares. KE pretty reliably charges on awards exactly what would be charged on a paid ticket.)