Ursegor
World Champion
He is 1 year older. That usually lowers the price of a player regardless of his talent. He will be 29 year old this September so no youngster anymore either. Aside from that the wish of a player, should he really want a move/demand it, will also influence the price. So he will not necessarily be sold for a higher amount than he was bought for (40m). 35m could do it, I believe.
Errr ... If PSG don't want to sell they won't sell, simple as. According to your logic Ronaldo would be available for a decent fee around € 50 million or so. 4 years older than when he was when he was bought for € 96 million with only 2 years remaining on his contract and public declaration of "sadness".
There is 0 % probability that PSG will make a loss on Silva after 1 season. They aren't retarded.