This sentence is not correct because of the grammar structure. This is a noun clause, which means it is a dependant clause. "Whatever they pay you" is supposed to be the subject since it is placed as the first part of the sentence; however, the subject in your sentence is "I". To have this sentence correct, just rephrase it this way: I'll double the price of whatever they pay you. I=subject, will double=verb, the price of=direct object of the verb "double", whatever they pay you=noun clause acting as both object of the preposition "of" and complement to the meaning of the sentence. In this example, this is correct since "whatever they pay you" is the object of the preposition "of". Does that make sense?

Hi Sinem, No, this sentence isn't correct. Here are two possible correct versions "Whatever they pay you, I'll pay you double" "Whatever they pay you, I'll double it." I hope that helps.

We would likely say "Whatever they pay you, I'll pay you double." or "Whatever they pay you, I'll double it." Either is correct