It's not elective. At least at present in the UK it is considered a medical necessity after extensive investigation.
In my case from the first time I spoke to my doctor to the first specialist appointment I had took 18 months - with the limited number of clinics that has for many extended to 4+ years before their first appointment. Then there are a minimum series of psychological interviews stretching over 18 months before being passed onto the doctors, then second opinions from a second psychiatrist etc etc. The whole thing can take up to 10 years for those with no private funds.
I attend a charity group where some 16-17 year olds attend whilst living in council accommodation,as they were estranged from their families, in towns where they knew no one and were regularity beaten up and abused and could afford to travel to the charity once a month. With years of a wait for an appointment, meanwhile unable to afford anti-androgen pills and physically growing into bodies they despise. Unable to obtain work and with an increasingly vocal anti-TG movement, I am surprised the suicide rate is not higher.
As to the US forces paying? The DoD medical annual budget is around $3.6B, the maximum TG estimated TG cost is around $8M, a rounding error in the annual cost and vanishingly small against the cost of VD treatment - which seems remarkably acceptable as a cost of doing business.