It seems obvious to me that you make the offer. As mentioned they could trade him after the "signing" (the mere act of agreeing is the equivalent of signing) although it wouldn't be easy to get equal value if other teams know they have to deal him. if you don't make the offer, you get NOTHING, not "equal value", in a trade, since there wouldn't be a trade. so the question to ask (assuming the Mets don't want him and would try to trade him if he accepts) is not about equal value - its about whether you would trade the dollars you are eating in the trade for the players you are getting back. If, for example, you think you'd need to eat 5 million to trade him to the Dodgers for Alex Wood the proper question is "would I trade 5 million for Alex Wood"? - because you never planned on keeping Walker anyway.