To estimate a maximum purchase price for the coin in question, we will consider several factors:

1. Current Condition: The coin has a condition of 85 (ebc-), which indicates that it is in quite good shape. This generally translates to a higher value compared to coins in lower conditions.

2. Previous Auction Prices: By looking at previous hammer prices, we can see that coins with similar conditions have reached varying hammer prices. For example:
- In 2023, a coin with a condition of 95 was auctioned for 2100 euros.
- In 2022, a coin with a condition of 80 was auctioned for 1200 euros.
- In 2021, a coin with a condition of 85 was auctioned for 1400 euros.

3. Starting Price and Average Hammer Price: The current starting price is 1600 euros, and the average hammer price in previous auctions is 1353.14 euros. This suggests that the starting price is relatively high compared to the average hammer price.

4. Auction Trends: The coin has been auctioned 21 times and has sold on all occasions, indicating consistent demand. Additionally, the fact that it will be auctioned again soon may influence buyer interest.

Based on these factors, an estimated maximum purchase price could be in the range of 1800 to 2100 euros, considering that the condition is good and there are precedents of higher hammer prices for coins in similar conditions. However, since the starting price is 1600 euros, it is likely that buyers will be willing to pay a little more, but not much beyond 2100 euros, unless there is exceptional interest in the coin.

Therefore, a reasonable estimated maximum purchase price could be 2000 euros.