His record for his country doesn't affect his value. Scoring against Qatar, Honduras, El Salvador and Bolivia doesn't add much weight in negotiations.
If Sancho was to be put up for sale this summer, there would be a market for him. Liverpool, Chelsea and probably City would all be interested as they were during his time at Dortmund. He signed for £73m last summer, I think they could get close to that figure this summer, no problem.
His market value is still much higher than Richarlisons because he is younger and has done it consistently at a higher level. Plus he is English.