The commander had paid a high price for his Roman citizenship. How did Paul say he got his?

Answer: He was born a citizen

The commander said, "I paid a high price for my citizenship." Paul replied, "But I was born a citizen" (KJV: "I was free born").

“The commander went to Paul and asked, “Tell me, are you a Roman citizen?” “Yes,” he answered. “I paid a high price for my citizenship,” said the commander. “But I was born a citizen,” Paul replied.”— Acts 22:27-28 (BSB)