https://www.fangraphs.com/blogs/j-d-martinezs-potential-for-falling-off-a-cliff/
Here's a long article from the Tribune. Doesn't say much of anything of note tho. Makes a case that he should be worth about $150M.
If you want to take the contract down to six years, then the number comes back at $150 million. Scott Boras might be looking for that extra year, but that year shouldn’t tack on another $25 million to $30 million. Martinez is unlikely to make up for that last year with his production in the first few.
Keep in mind, I’ve used only hitting comps to arrive at these numbers. For the most part, baserunning and fielding do not favor Martinez. We don’t have to ignore those two aspects of the game to get J.D. Martinez his $150 million, but we have to discount how bad the numbers make Martinez look. He can be a below-average baserunner and defender and still return a $150 million investment. He just can’t be as bad as his numbers last season or over the course of his career indicate. I think it is fair to expect two more really good seasons from Martinez. After that, the range of outcomes is enormous. Expecting good production in 2020 is a risk that any signing club is going to have to take.