Look on eBay or other selling sites? A good quality secondhand one will last longer than a cheap new one.
You may need the services of a decent Taylor but decent weight / quality of material and cut are good things to notice. You should be able to find one for around £100, new can be anything from £79 to £400 Plus. Personally I think it’s worth investing in better quality which will last another 20 years plus. I have some that are at least 30 years old and still look ok worn for various activities by people in need of a jacket.
I got a fantastic Alan Paine jacket on ebay recently, for a fraction of what it would have cost new. There are lots on at the moment. Vinted is pretty good too.
I did dream of hacking in traditional fawn breeches and tweed jacket as people used to when I was a child longing to ride. But (and it is the same with walking clothes) I ended up with modernity - goretex, breatheable and rain proof for both summer and winter. with a bp and high viz as well.