Updated: Feb 1, 2019
This pay stub I found on Archive.org shows a Corporal's pay was $13 per month. "William H. Yerkes" is listed in the History of Pennsylvania Volunteers, Vol. 3, p. 29. The pay stub shows his salary was $13 per month. He was paid for 1 month 18 days, receiving $20.80. (Clicking the image will take you to Archive.org)
According to CPI Inflation Calculator, $20.80 in 1862 had the purchasing power of $517.13 in 2018.