Ok lets take Gayle, 50k a week and has made 6 appearances for newcastle this season, all as a sub, scoring once
If he is out of contract at the end of the season where is he going to go? He cant get a game for the Toon, who are struggling so who else is going to take him? The idea he is going to be earning 50k a week on his next contract is pie in the sky! He will go to the highest bidder sure, but that might not be for very much money. He's hardly got a stellar record in the PL - 11 goals in 5 seasons for Poocastle and 26 goals in 125 appearances in the PL - so his chances of another club there are limited, even for whoever gets promoted.
At champo level he looks good but who can afford to pay him more than 10-15k a week? probably nobody. ultimately his wages are only going to be what somebody is prepared to pay, and for Gayle, thats unlikley to be out of reach of champo clubs