The partial 1918 Toney is a good comp:
112 IP
0.73 WHIP
.192 OAV
0.74 BB/9
Doesn't get much closer than that. Of course the K/9 are way off (Toney is 2.00 K/9).
Toney currently costs $5,086,083, but that's AFTER 2 consecutive bumps (I think) in the salary adjustment. Assumedly Kershaw's initial salary will be strictly based on the old formula, and then he may be adjusted over time based on usage. I think ~$5.1M is the rough ballpark for Kershaw.