Expensive? It can be.,, but often isn't
Our local (council) courts cost £20 per person per year. There's 4 courts, you can book them for free on an app
Lessons in a group are £7 pp
Rackets are cheap. You can find them second hand too very easily. You can come in shorts, a t shirt and any old trainers
Tub of tennis balls is £5
All quite accessible really IMO
A smarter local club I go to is £60 per year and runs free mix-ins three times a week, where anyone of any level can just turn up and play. It's very popular.
If you want private coaching that is expensive but still cheaper than , for example, a PT
In my experience it has been a very accessible sport to get into at an older age