Surveying Services - Cost Differences

That can probably be predicted already.

Not necessarily. I personally know of a case where a builder, whose site plan was justifiably rejected due to gross errors, was able to pick up the building permit within one day (!) after submitting corrected construction documents because of his complaint.

all across the republic

It must be said that the understanding of the official site plan varies greatly across the republic. For example, in Rhineland-Palatinate, it simply means an excerpt from the cadastral map, while Baden-Württemberg distinguishes between qualified and simple.

I rather believe that 99.9% simply have the official one made

..., because it is simply more convenient for planners and examiners. Those who should know better have no interest in informing the builder. Which builder even has surveying services on their radar and makes the effort to obtain quotes when the planner takes care of everything. Here, of course, it is up to the surveyors to offer the services required for the respective construction project. However, the original poster specifically requested the official site plan, which is then of course only offered — at least by those who are allowed to do both.

But I will ask my contact at the cadastral office whether one could get any other answer than "We don’t know." from them.

Oh yes, that interests me!

Exactly. You budget the approximate costs under incidental construction costs, request quotes from 2-3 surveying offices, and are happy that the offers stay within the range.
Very few people investigate further to see if it could be cheaper.

Correct.
I also inquired with three different surveyors and was lucky that one of them immediately submitted a fair offer that met the requirements.
Although this person is also a publicly appointed surveyor, he directly submitted an offer that was about 1000 EUR cheaper than the other two. Upon my inquiry, I received the following statement:

"Apparently, the surveyor colleague included the creation of an official site plan in his offer. However, such a site plan is only required under certain conditions, must be billed according to the fee regulations, and is usually significantly more expensive. Nevertheless, all information and entries required for the building application are definitely included in the 'normal' site plan. An official site plan is, for example, necessary if the building plot has not yet been formed (which we can exclude here) or if building encumbrances are or will be registered on the building plot."

How now? They must be able to say whether the boundaries have been determined and what the quality of the coordinates is. And if there is only the statement that this information is only provided upon formal request for a fee.
VVBauPrüfVO:
When issuing the property map/cadastral map, the cadastral authority also informs, upon request, whether the facts mentioned in paragraph 3 numbers 1 and 2 apply.

Oh, many thanks for pointing out the VV.
That would then solve the mystery about numbers 1 and 2 from paragraph 3.

Next Thursday is the notary appointment for purchasing the property, afterwards I will apply for the cadastral excerpt with the aforementioned information (unfortunately costs €30).

Then I will (hopefully) have black on white that we do not need an official site plan. Because there are no encumbrances on the property (excerpt from the encumbrance register/land register is available). There are also no boundary encroachments, the old site plan from 2005 clearly shows this.

Many thanks also for the hint not to split the order between two surveyors.

Ps: I absolutely do not want to badmouth the employees of the building authority/cadastral office.
From my own experience I can report that in such cases the famous discretion by the caseworker at the office is then generously used.

Excerpt from the register of encumbrances/ land register is available

The wording is somewhat misleading. One might think that the register of encumbrances and the land register are connected, which they are not. If there are no encumbrances, there is no excerpt from the register of encumbrances. I assume you have the explanation from the building supervisory authority stating that there are no encumbrances in favor of or burdening the property.

By the way, I have to praise the Marzahner office. They called me and said that nothing was included and asked if I really wanted a written statement about it (subject to a fee). I didn’t need it at that time, so I simply did nothing further / didn’t have anything done.

The spelling is somewhat misleading. One might think that the Baulastenverzeichnis and the Grundbuch are connected, but they are not. If there are no Baulasten, there is also no extract from the Baulastenverzeichnis. I assume you have the explanation from the building authority stating that there are no Baulasten in favor of or against the property.

Yes, exactly.