The AIPLA Report of the Economic Survey for 2017 notes that the typical patent infringement suit with less than $1 million at stake costs on average costs more than $600,000 dollars, while the typical patent infringement suit with between $1-10 million at stake costs on average nearly $1.5 million to litigate.

https://blueironip.com/what-are-the-costs-to-enforce-or-defe...

Costs for IPR or Post-Grant Review (approximate mean):

    Through filing petition: $120,000.
    Through end of motion practice: $300,000.
    Through PTAB hearing: $400,000.
    Through appeal: $600,000