What dates did you search for that particular fare? I can’t seem to find any so cheap.That really depends on how much you value QF points. The best way to calculate that is to take the cash fare price you would pay for the price, subtract the taxes and fees you would pay on the classic award booking and divide the total number of points by the cost of the cash fare. Generally, anything over 1 cent per point value is considered good, although I've gotten that value as high as 9 cents on flights to LDH.
Also, if you're paying 350,000 points on a one-way business class ticket to Singapore you are likely paying too much. A classic award business award on QF should set you back 75,000 points + taxes & fees one-way:
View attachment 277480
Or are you QFF gold member or something?