I'll have to spend some time thinking of what an extension would look like. Haven't done that. But I'm pretty sure both sides can find a number they like.
While I don't think it matters from an Oriole perspective, any team adding Trey could certainly consider working on a contract longer than 2022.
The reality is RHed 1B bats aren't generating a lot of contract interest. For example, a decent comp could be CJ Cron. Since 2017 he's been on the Angels, Rays, Twins, Tigers and Rockies (a year apiece) and has been non-tendered contracts thru arbitration since the Twins. He's actually put up good numbers, but we've seen a handful of guys like this get put back on the market. CJ Cron, despite some success in limited PAs last year, signed a minor-league deal with the Rockies. He's making good on that, but why - at 32 - would his contract fate be any different than it's been in recent years? He's been a FA on the market the last 2.
Trey is a little younger than Cron, but Cron was getting non-tendered (after a 25 hr, .780 OPS season) at the age same age.
Mancini offers more than Cron. I think he's probably a more complete hitter and has some positional flexibility (even if he's not a good OFer) that Cron can't offer. Perspective on his Leadership and story could have some perceived value at least in terms of creating an extended contract.
Trey probably gets something around 7.5M in ARB3 next year. If you added 2 years at 9M apiece and included a 1M s/b and a 3.5M b/o on 12M team option(s), that's a 3/30. That's the type of deal a MIL or CLE could handle. If you wait for a larger payday, you might not get the chair you were hoping for when the music stops.
I think I said 4/40 or 5/50 a year or more ago, so that's largely the same thing accounting for some of the uncertainty of the last year+.