You're looking a little too far ahead, I reckon. I'm eyeing the same dates and destinations, planning to travel up to Birmingham by train to catch BHX-SGN-BHX to get two badges. There's little point in tracking prices at this point of time because QR usually releases promotions monthly, from 3 months up to a month prior to departure in my experience.
I was very tempted by a reported under £1200 MUC-HND which would get the 3rd & 4th badges, supplemented by some JAL flights booked on Avios for Christmas in Micronesia but decided to wait and see what other sales come along later in the year.
I have booked ARN-JNB//CPT-TXL today before the specific sale fare vanishes tonight, securing the first two badges. Not ridiculously cheap but a keen price & where I want to be when !
The AMS-JNB-AMS sale fare mentioned in the previous post is lower but implies it requires 2 people as is marketed as a companion fare. Haven't tested it.