What measures do celebrities take to protect their images from being used for commercial purposes without permission? How much does this typically cost them?

From a legal perspective, they rely on the various state and federal laws that give them actionable claims against people/businesses that use their images without permission. A few examples of these laws are:

Right of Publicity Laws - Varies by state. Some states have statutes that specifically forbid using a celebrity’s likeness (and even voice) for commercial use without appropriate permission.

Take the lawsuit through trial ($XX,XXX to $X,XXX,XXX+)

Erin Blanchfield backtracks on labeling Maycee Barber 'unprofessional' after seizure canceled UFC Vegas 107 fight - Bloody Elbow

Common Law - Varies by state. Many states recognize what are known as “the four privacy torts,” which include “appropriation of another's name or likeness.”

Send off a Cease & Desist demand ($XXX to $X,XXX)

File a lawsuit and push for early settlement ($X,XXX to $XX,XXX+)

Atheists who said that reading the Bible made them an atheist, how? Literally there are millions of people who read the Bible daily and still believe in God. So why say that? I mean unless you want to sound smart & edgy

The Lanham Act - Federal. While the Lanham Act is generally thought of in the context of Trademark law, Section 43 has a provision regarding “false endorsement” that has been used by celebrities (notably, Carmen Electra) to fight the unauthorized commercial use of their likeness.

As far as the cost goes, that will vary depending on how far the celebrity has to go. Aside from the deterrent effect created by the mere existence of the laws (cost = $0), a celebrity may need to hire a lawyer to: