We have url's like this: /demand/change_db_value/18050/13/.80/0/cost

Notice the /.80

In our nginx conf for our site we have this access rule: location ~ /\.ht { deny all; log_not_found off; access_log off; }

This rule produces this error in the logs: error.log: access forbidden by rule, server: oursite.tld, request: "GET /demand/change_db_value/18050/13/.80/0/cost HTTP/1.1"

We want to of course block access to any .htaccess files or files beginning with ".", but how do we make an exception for this particular url structure?

Try matching to the start of the URI, i.e. location ^/\.htaccess {...