I think the secret is not giving elite contracts to anyone, especially pitchers, because then you end up in these types of messes. I think they were right letting Lester walk. They were wrong signing Price, and probably Sale. Of course they had no choice to pay for SP because they haven't really developed any.
Lester in Chicago: 5 seasons, 150 GS, 893.0 ip, 3.48 era, 3.74 FIP, 1.216 WHIP, 8.6 K/9, 2.5 BB/9. ERA+ 120
Price in Boston: 4 seasons, 102 G/97 GS, 586.0 IP, 3.85 era, 3.74 FIP, 1.205 WHIP, 9.3 K/9, 2.4 BB/9. ERA+ 117
Lester's last 3 seasons as a Cub have also been considerably worse than his first 2 seasons. 3.97 ERA/4.22 FIP, 109 ERA+, 21.9% K%, 7.4% BB%, 3.4% HR%. OTOH, His K% rebounded a little this year and he's close to his lowest BB% of his career too.
Price in that same period is at 3.77/3.83/121 ERA+, 25.6% K%, 7.1% BB%, 3.2% HR%. This year, Price is at a career high 28.0% K%.
Back to Mookie, if he wants 10/360, they should trade him. There's hard to see any excess value there and breaking even would be a good outcome. A lot of his value is tied up into defense and unless you think he's going to hit at 2018 levels, I can't see him (or really any player) being worth that much.