Lets answer both.
Ketel Marte is a 3fWAR 4 bWAR player right now making an average of around $15 million the next 4 seasons. He would cost you an arm and a leg given his current production. He's likely not available.
Starling Marte is hitting better than he has in a while, but is 35 years old and owed over $20 million next year. His defense has taken a major hit and the bat has only slightly made up for it. He would cost you almost nothing and is likely very available. The Mets would also have to throw in a lot of cash.