I'd certainly look to extend him. FanGraphs used to show the "worth" of a player in terms of dollars, but it doesn't look like they do any more.
Though, "prior Verdugo" has been roughly a 2 WAR player each of the prior 4 years (1.8 fWAR vs 2.125 bWAR on average). Last I knew, the "value" of a win was about $8.5m (
https://blogs.fangraphs.com/what-are-teams-paying-per-war-in-free-agency/), which would make him about a $17m per year player, in terms of value, averaging out the two.
Edit - what I'd use for a comp when approaching Verdugo about an extension is the deal Bryan Reynolds just got from the Pirates. FWIW, Reynolds has an all star selection (if that matters) but I think anyone would agree is a superior player to Verdguo. However, he also had (I think) about 2.5yrs left when he signed his extension and Verdugo only has 1.5 left, though Verdugo is the younger player. I'd tell him you think he's a comparable player, but "more valuable" to the Red Sox so offer him $110m over 7 years ($15.75m per year) compared to Reynolds $106m over 8 years ($13.25).
@BaseballJones - Miami got Jesus Luzardo from Oakland for a 32yr old Starling Marte whom had put up a 2.8 bWAR in Miami the first half of the year in 2021. Not for nothing but Marte had a track record of being a superior player, obviously, did play CF (not irrelevant) but he also was 5 years older and only had 2 months of control left (also not irrelevant). For comparison, Verdugo (to this point) has already accumulated a 2.8 bWAR.
If one assumes the positives for Marte (track record, defensive position) and Verdugo (age, contract status) roughly even out, I'd be very upset if the Red Sox moved him for anything less than this kind of return, certainly. Without thinking of "fit" but just in terms of what is applicable now to Luzardo in 2021, maybe something like Grayson Rodriguez (top prospect; some injury history; tough major league performance to date but wildly talented).