I do think that something people aren't taking into account, relative to Crochet and an extension, is how his career up to this point as a relief pitcher has really kept his earnings down.
Assuming Spotrac can be believed (and I have no reason to think otherwise) it's not like he's been Fried going from year to year with huge success as a starting pitcher early on in his career to prop up his earnings. He got a nice signing bonus, for sure, but has "only" made about $8m in his career up to this point, and will probably "only" be around $11m after his arbitration award this year, if it went to arbitration (which I don't think it would).
$11m is a lot of money in the real world, but in terms of baseball players, Fried surpassed that total alone with his contract in his 4th year (which brought him up to a career earnings of around $28m (factoring in his bonus). If the Red Sox offered him something along the lines of 5/$125m/$25m (options or not) he'd be kind of crazy not to take it. Fried got about $27.25m AAV, so $25m AAV might need to be bumped up a little, but at $25m you're talking very close to market value.
As mentioned, that would put him as a free agent at the same age as Fried is now, but with multi-generational wealth in the bank. This is a scenario where the idea of an extension at AAV market value (ish) and 5 years makes a ton of sense for both parties.
https://www.spotrac.com/mlb/player/_/id/48366/garrett-crochet
Or, put another way, I'm right in line with about what
@YTF is saying. Something with an AAV of around $25m and maybe there is a player option for the 6th year or some such. Again, Crochet has "only" made about $8m to this point, and going year to year would probably "only" be around $20m all in, assuming he continues to dominate.