Regulation and the right ammo or loads for the rifle is part of owning a double rifle, so sorry its part of the deal.

Unless it is a "self-regulating" rifle where wedges can be modified on the barrel by the user. These tend to be on the cheaper side of the range.

A rifle might be regulated for a particular factory load, but with handloading it usually is possible to find loads that duplicate the results.

Some other guys can comment on their Sabattis or other brands that you mention.

The second hand market would be the place to look for a good deal. In Europe I would think it might be possible to find a good second hand rifle that is almost brand new/used only occasionally from a hochsitz.