The overall associated notary fee is typically 1,5-2% of the purchasing price. The cost is lower, the higher the purchase price is, and the higher the mortgage amount. To be more precise:
The fee for the purchase is about 1,1% for a house of 200,000 and declines to about 0,9% for a house of 1 million.
The fee for the mortgage passing and registration is about 0,6% for a mortgage of 200000 and declines to about 0.5% for one of 1 million.
Adding a second mortgage component (eg a KFW loan of 50,000) will add about 200 Euros to the cost.
Among other things, the notary will take care of drafting the purchasing contract, entering the buyer in the land registration and generally taking care of all communication with the German tax office.
This fee estimate includes the cost of the registration in the land registry.