I do think their muscle would still be significantly reduced by the hormones, but the older someone is the more their body is “set in place.” This means any changes will take longer to occur and they may not happen to the degree that they would have if they started younger. So someone starting mid 20s - 30s likely won’t have skeletal changes, since that part of their body has already finished growing. (Someone starting as a young teen definitely will have skeletal changes though.)
I’m trans in the US. After insurance I pay about $300 to $400 every 3 months for blood tests and a follow up. My meds cost me an additional $90 for 3 months as well. They are my hormones and another medication unrelated to me being trans. I get my meds at a local independent pharmacy, so they are relatively cheap. I used to get them at a large chain pharmacy and they were about twice as much there.
I also used to work as a cashier at a pharmacy. I once had to ring someone up who was paying over $3,000 for some cancer medication. It also wasn’t uncommon to see people paying around $500 for medications that they need to be alive.