At this price point, even if they are launching a sale, it's unlikely this specific flight would be available at sales price. The plus bundle can be good value though.
To skip the check-in line, you will need to use the airport express train and do in-town check-in. Usually, there are minimal lines there, and you can do it any time on the same day so you can maximise your air-side time, if that floats your boat.
If you don't mind a later arrival, you can also try MH as mentioned. As a WP, you can have your dining fix from 6pm at the MH KUL satellite lounge, although keep in mind you'll need to take the APM back to the main terminal for the flight to SIN.
Most of the 3K flights I've been on between SIN/HKG get quite full, although the last SIN-HKG flight I was on last week had a load of 72.2%, plus about 12 people no-show. This is despite having cut from 3 to 2 flights daily.
Also, keep in mind that you'll board/deboard via stairs in HKG. You then board a bus that takes you to the main terminal. Although if the airport is extremely congested, or if there are other operational issues, you might be lucky enough to use the satellite gates.
If you're going to use the QF lounge, when you get out of the front doors, use the first set of elevators you see, and go to level 4 (bottom level that can be accessed). You'll be in the general area for the boarding gate as soon as you step out of the lift.
Interestingly, Tiger uses the aerobridges just like most other airlines so it doesn't feel as cheap as nasty. They now also use T2 at SIN.