I tried to just count major/key players or big contracts plus a few role players. I didn't include Thornburg, because he never pitched for us and is recovering from a very serious injury.
Here's an updated & expanded look...
Current Core of this team:
(Note: "to keep him" could also mean to replace him with a similar level player through free agency.)
Kimbrel $13M then $18M to keep him (+$5M)
Pomeranz ~9M then $19M to keep him (+$10M)
Sale $25.5M + $13.5M then over $30M to keep him (+$18M)
Bogey ~$7M & $12M then maybe $22M to keep him (+$10M)(+$15M from 2018's salary)
Porcello $21M + $21M then maybe $16M to keep him (-$4M)
Betts ~$10M, $15M, $20M then $28M+ to keep him (+8M) (+$18M from 2018)
JBJ ~$6M, $10M, $14M then maybe $18M to keep him (+$4M) (+$12M from 2018)
Pedroia $13.75M until the end of 2021
Price $31M until the end of 2022
Beni: 5 years of control (3 are arbs)
Devers: 5+ years of team control (3+ are arbs)
Role Players:
Kelly ~$4M then maybe $7M to keep him (+3M)
Thornburg $2.05M + 1 more arb (hard to project)
Holt ~$2M then 1 more arb (DFA?)
Vaz ~$1.5M then 2 arbs
Smith ~$1M then 2 arbs
Leon ~2.5M then 2 arbs
Wright ~$1M + 2 arbs
Workman ~$1M + 2 arbs
ERod ~$4M + 3 arbs
Not Yet At Arb
Barnes & Hembree 1 the 3 arbs
Swihart 1 then 4 arbs
Scott, Hernandez, Marrero 2 then 3 arbs
Arb Years Not Set
Lin, Maddox, Travis, Velazquez, Johnson, Taylor, Beeks, Brentz, Shepherd, Buttrey, Jerez, Owens
Sunken Cost Coming Off the Books
HRam $22M after 2018 or 2019 (if he vests)
Pablo $19M to $5M for 2020 then zero for 2021
Castillo (off luxury tax) $11.8M, $11.8M & $14.3M
Of course, we do not need to keep everyone to be competitive, and we could replace some of these players with lesser cost free agents.
If my projections are wrong, and players will not be making what I estimated, it would also mean their value has fallen due to poor performance between now and then.
I'm looking at over $55M more needed (after last arb or year of salary) to keep everyone and fill no holes that might open elsewhere. It will likely be more than $80M from their 2018 salaries. Subtract the sunken costs from HRam/Pablo & Castillo and it doesn't look horrible, but it will still take a massive increase in our budget to keep everyone or replace them in kind.