If my quick maths are correct, there's currently €14.8m of his 2017 €222m transfer fee left on their books*, so I would expect that to be the around the number they ask for as a transfer fee.
The motivation for PSG here is offloading his wages because they can't afford Neymar+Messi+Mbappé's new deal while also having a functional competitive squad around them.
Like Juventus selling Ronaldo, the fee is an afterthought.
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Quick maths working out, please correct me if I'm wrong.
Signs for €222m on a 5 year deal. 222/5 = 44.4
2017, 2018, 2019, 2020 amortisation = 44.4m pa.
Signs 3 year extension in 2021
2021, 2022 amortisation = 14.8 pa
Outstanding amount = 14.8