It depends...Do you want your league to mimic MLB in its current state? If so, set it to $100M and let the bigger market teams sign more free agents,etc. Having more cash frees allows a team to go in the red year for a few years with high salaries.
I am in two solo leagues and have 1 set at $100M and the bigger market teams seem to "dominate"
The other league is set at $30M (Why 30, I dunno

) and it seems to create a more level playing field.