FlyerTalk Forums - THY Now Offering Paid Discounted Airport Upgrades

Seems to be offered from outstations only. Examples:

Germany-IST Y->C EUR 200
Germany-Turkey Y->C EUR 250
TLL-IST: Y->C: EUR 150 (Dec.2017)
HEL-IST: Y->C: EUR 150 (2017 still the same 3/2022 )
MAN-IST: Y->C: USD 250 [173 GBP] (2016)
RIX-IST: Y->C: EUR 200 (2016)
TBS-SAW: Y->C: EUR 150 (2018)

TPE-IST: Y->C: USD 850 [TWD 29k] (2016)
DEL-IST: Y->C: USD 300 (2015)
DEL-IST: Y->C: USD 425 (2017)
BKK-IST: Y->C: EUR 749 (2024)
BOM-IST: Y->C: USD 300 (2014)
BOM-IST: Y->C: USD 400 (2016)

ICN-IST: Y->Y+:EUR 250 (2015)
ICN-IST: Y->Y+:KRW 55k [about USD 500] (late 2016)
IST-CLJ: Y->C: EUR 120 (2024)
HAN-IST: Y->: USD 500 (2018)
HKG-IST: Y->C: EUR 750 (2018)

HKG-IST: Y->C: EUR 750 (March 2016)
HKG-IST: Y->C: EUR 750 (2015)
HKG-IST: Y->Y+:EUR 400 (2014)
HKG-IST: Y->C: EUR 800 (2014)
KUL-IST: Y->C: USD 520 [MYR 2k] (2018)
MNL-IST: Y->: USD 500 (2018)
NRT-IST: Y->C: USD 570 [JPY 60k] (June 2016)
NRT-IST: Y->C: USD 300 (2014)
SGN-IST: Y->: USD 500 (2018)

IAD-IST: Y->C: USD 500 (2015)
JFK-IST: Y->C: USD 1000 (2015)
JFK-IST: Y->C: USD 500 (2016)
JFK-IST: Y->C: USD 1099 (2021)
ORD-IST: Y->C: USD 999 (2015 and 2018)
IAH-IST: Y->C: USD 999 (2015)
IAH-IST: Y->C: USD 750 (2014)
IAH-IST: Y->Y+:USD 300 (2014)
IAH-IST: Y->C: USD 999 (2017)
LAX-IST: Y->C: USD 999 (2016)
LAX-IST: Y->Y+:USD 350 (2015)
LAX-IST: Y->Y+:USD 300 (2014)
SFO-IST: Y->C: USD 1299 (2015 also Nov 2023)
SFO-IST: Y->C: 699 to 999 based on the C-class load (2017)
YYZ-IST: Y->Y+: CAD 361 (2016)
GRU-IST: Y->C: USD 749 (2017)
MRU-IST-MUC: Y->C: EUR 800 (June 2022)