Hello,
I still have a few ideas/remarks:
Der Bodenrichtwert ist 250€/m².
That already makes the matter look completely different again. With that, you are in the highest and therefore most expensive category for the standard land value. If you really want to have all 7 points boundary-determined, you are looking at around €4,000 for the measurement. As a note: You do not have to have all points determined! You can also have only 2 done.
According to the picture, there is a boundary point on the right side at about the middle height—is that a bend?
Another option and very likely much cheaper: the official boundary information. However, several factors play a role here, such as the quality of the coordinate. Whether this option is feasible I cannot say without knowing the surveying documents. The costs for the boundary information depend on the time required + basic fee. For 6 hours of on-site work + evaluation, you would be at about €1,500.
I estimate that this option would also be sufficient since you only want to build/plant a fence or hedge.
Again about restoring boundary points: The boundary points may be under-marked. If the stone is missing, the stone can be restored this way. Otherwise, the older boundary points were measured on surveying lines and can be restored accordingly.
If it should ever become more concrete, contact the cadastral office or the publicly appointed surveyor of your trust and ask for a cost estimate.
Note: There is freedom of choice of the surveying office. That means: Suppose you live in Wilhelmshaven. You can contact a publicly appointed surveyor from Hanover. This person may not refuse the order.
If you have any further questions, feel free to ask.
Niels