I am not sure how long of a MR you want....I often take SK from BKK-SIN in J class, it's only about US$210 RT, and it's on a newer A340. It's only about 1800 miles RT, though if you have BD for your *A miles, then that doubles.
Otherwise, it's not so amazing for sudden fare sales, since now TG and SQ both don't allow mileage on their cheapest fare classes (W on TG, and most cheap fares on SQ). When they match the new LCCs on routes within Asia, they use non-mileage-earning fare classes.
Still, BKK-SYD on TG and SQ is about $625 all in (using a miles-earning fare class), which is not bad considering it's about 8,500 miles RT on SQ.