Quoting: villenash
If Graves puts up a similar season next year, then he will have much more trade value than he does now. He definitely played well this year, but teams aren't going to give up a player like Tatar for him.
Jost has been in the NHL consistently for the past 3 years now. His ice time has decreased in all 3 seasons, he doesn't have great underlying numbers, and he doesn't put up many points. He was also drafted as a center and is awful in the faceoff circle -- so he's a winger at this point. He also doesn't play the penalty kill. He does get around 2 minutes of PP time per game over the past 3 seasons, but he still doesn't produce. The only thing going for him right now is his age - 22. He's still young and he could turn it around, but I don't see any team giving up a lot to get him. He would be a great buy-low candidate, but would the Avs even want to give him up for a low-ball offer -- probably not. So I don't see him being traded anyway.
Tatar was previously traded for a 1st, 2nd, and 3rd, to VGK from DET -- which was an overpay at the time, but he has since put up his best offensive numbers to date. The trade proposed by OP is weaker than a 1st, 2nd, and 3rd. Jost + Graves for Tatar just isn't fair value in my opinion.
I agree that Graves will probably have more value next year, which is why I think it would be better for Colorado to hold onto him at least one more year. That also allows Byram the opportunity to settle before we push him into the top 4.
Jost has shown improvement in CF% and FF% this season, as well as flashes of offense when given the opportunity (eg. 7 points in his last 9 games prior to the lockdowns). He's also at an age where many top 6 forwards enter the league, yet he already has 3 seasons under his belt. At the very least a team would get a solid defensive 3rd liner, and at a cheap caphit that has some good value. He was also eased onto the PK late in the season and did well in the role. The only reason why he doesn't get more PK time is because Colorado have an embarrassment of good defensive forwards who are more experienced than Jost in that role, but there's no reason why Jost can't be an effective PKer. In fact I'd be surprised if he doesn't become a regular PKer at some stage given how reliable he is with the puck and on the forecheck (as evidenced by his 71:31 takaway to giveaway ratio).
As for Tatar, just because Vegas overpaid massively for him doesn't mean that that was his value at the time. Nor does it mean that a similar package this time around would be an underpayment. A 1st + 2nd + 3rd would be good value for a player like him. Also bear in mind that on most contenders he wouldn't be a 1st line winger or get PP1 time (certainly not on the Avs), nor was he a 1st line winger prior to his 2 seasons with Montreal, so that has to be taken into consideration when considering his offensive output.