Scientific American cites studies saying that the additional medical cost of transgender soldiers is between 2.4 million and 8.4 million per year. That is literally nothing, less than the cost of toilet seats.
https://www.scientificamerican.com/article/cost-of-medical-care-for-transgender-service-members-would-be-minimal-studies-show/

https://www.theguardian.com/us-news/2017/jul/26/trans-health-cost-us-military-budget-pentagon