Start with his advanced stats and use the # numbers. Adjust for ballpark by multiplying AVG# by ballpark adjustment from the chart here:
https://www.whatifsports.com/forums/Posts.aspx?topicID=519598&threadID=11831435#l_11831435
You can see draft and performance trends here: to give you your $80m average performance for all players:
https://www.whatifsports.com/mlb-l/stat_snapshot.asp
I then estimate a point of average per extra $1m in cap, so drop ~10 points and then adjust slightly down because his AVG# was below $80m performance trend baseline.
For OBP, I start with his BB/100# and adjust for league salary by reducing by the salary factor (80/90=.111, so his rate drops from 11/100 to 10/100) times his average PH PA. Subtract the BB to get AB and multiply by the AVG above to get H. Reconfigure OBP from that new H+BB total for his average PA. If no history, then I take actual PA+11% with a cap of 760 PA.
I could probably get more accurate salary adjustments, but these are good enough for quick estimates and comparisons.