I read your question.
Even if you say permanent memorial service in a nutshell, there are actually various forms.
For example, there are things called “joint ossuary cemeteries” or “joint burial grounds.”
This is a place where many bones are buried in one place on the site of a temple or in a graveyard to make a memorial service.
In this case, there is no need for cemeteries, tombstones, or ossuaries.
However, since the bones of those who have died will be buried in the same place as many others, it is impossible to have them returned at a later date.
This form is probably the cheapest, and the market price is about 30,000 to 100,000 yen per unit.
Another method is to rent a graveyard and build a tombstone.
If you choose a general area and materials for tombstones, it is better to think that it will cost about 150 to 2 million yen.
However, in addition to that, it is normal that a management fee is charged every year, and if it is delayed, there is a possibility that it will be forcibly removed depending on the graveyard agreement.
As long as you keep paying the management fee, it is basically possible to use it permanently.
I don't really understand the meaning of the permanent memorial service that Nanohana mentioned, but does that mean they want to continue using the graveyard forever without paying the annual management fee?
If that's the case, I haven't heard many such forms at graveyards, so I'm sorry, but I'm not sure about the market price.
Also, in the case of an ossuary, there is a form where an annual management fee is unnecessary if a fixed amount is paid.
However, there are two things to keep in mind.
The first one may be separated into a family ossuary board and a personal ossuary.
Even if it's called a personal ossuary, there are places where you can put the bones of a few people.
If it's a permanent memorial service for a family ossuary, it's probably about 1 to 2 million yen.
If it's a personal ossuary, it's probably about 500,000 to 1 million yen.
The second is an eternal memorial service, but there are cases where the period is limited.
There are places called permanent memorial services where you keep them for 50 years, and there are also places called permanent memorial services where you keep them until the temple or hall is gone.
If you are concerned about the period, be careful.
This is my personal opinion, but I would appreciate it if you could use it as a reference.