200k a week on a free would be around what we'd pay in fee and wages on Guessand for 4 years as an example. He's not going to signing for 100k a week for anyone.
Tielemans and Kamara were supposedly £150,000 per week, and if Sancho signs I expect he'd be getting somewhere around the same level as them when they came in without a transfer fee.
He'd probably get similar at Dortmund or a big Italian club. He'd be better off financially in Turkey.
So it just depends where he wants to draw the line between cash and sporting merit.