LHR - DOH (QR10), ~2,000 GBP ($2,374 USD)
DOH - SIN (QR942), 811 GBP ($963 USD)

Was offered DOH-SIN 2 days before the flight and took it. I think this is reasonable value.
LHR-DOH was offered <12 hours before the flight. Didn't take it.

Overall worked out really well. Economy on the upper deck on the A380 for a day flight is fine. Albeit the wifi sucks
Connecting onwards in QSuites, was an overnight flight and ime sleeping on this leg is pretty vital to avoid jet lag if doing EU-SEA