I think Jack Hughes is probably the best example. He had a similar level of expectations, talent, and performance over his first couple seasons.

The main difference is that Hughes signed his extension before his breakout season while he still had a year remaining on his ELC. For that reason, he "only" got $8M. Had he waited for his ELC to expire, he would have had his breakout PPG season under his belt and would have cost $10M+.

Byfield's breakout season, while great, isn't as good as Hughes' was, so I don't think he'll get $10M+, but I do think he'll get more than $8M. If I had to guess, I'd say an 8 year extension would probably cost the Kings around $9M-$9.25M.

DeBrincat, Bratt, Kyrou, Tkachuk and Laine were all a bit older and signing their third or fourth contracts.

Would be the comps I'd use....

Quinton Byfield.........21.9 yrs old, 0.70 ppg, $X.XXm x X years
Matthew Boldy..........21.8 yrs old, 0.69 ppg, $7.00m x 7 years
Cole Caufield.............22.4 yrs old, 0.78 ppg, $7.85m x 8 years
Dylan Cozens.............22.0 yrs old, 0.88 ppg, $7.10m x 7 years
Clayton Keller............21.1 yrs old, 0.57 ppg, $7.15m x 8 years
Josh Norris.................23.2 yrs old, 0.83 ppg, $7.95m x 8 years
Tim Stutzle.................20.6 yrs old, 0.73 ppg, $8.35m x 8 years
Nick Suzuki................22.2 yrs old, 0.73 ppg, $7.89m x 8 years
Andrei Svechnikov...21.4 yrs old, 0.76 ppg, $7.75m x 8 years

I like yours better than mine lol

I also Think that the Byfield contract will be somewhere between $7.50m and $8.00m for 8 years. I would be very surprised if it would be more than Stützle's contract. Surely, their contract will be similar.
I expect Spence to get something between $1.50m and $2.00m for 2 or 3 years. Just saw again in last nights game against the Flames, that Arvy is great, when healthy, BUT he missed way too many games and his health is a big concern. I really like Arvy a lot and hope the Kings can maybe resign him for something just below $4.00m for another 2-3 years. I'm wondering, what other teams might be willing to offer him.