To estimate a maximum purchase price for the coin in question, we can analyze the provided data:

1. Current starting price: 800 euros.
2. Average starting price in previous auctions: 612.5 euros.
3. Average hammer price in previous auctions: 1038.33 euros.
4. Auction history: The coin has been auctioned 6 times and has sold in all of them, indicating consistent interest.
5. Condition: There is no information about the current condition, but previous hammer prices varied according to the condition, with condition values ranging from 10 to 85.

Analyzing the previous hammer prices, we can observe that:

- In 2020, the hammer prices were 600 euros (with condition 80) and 650 euros (with condition 85).
- In 2021, the hammer prices were 680 euros (with condition 85) and 600 euros (with condition 70).
- In 2024, the hammer price was 1600 euros, but with a very low condition (10).

Since there is no information about the current condition, it is difficult to make an accurate estimate. However, considering that the average hammer price is 1038.33 euros and the starting price is 800 euros, a reasonable maximum purchase price could be in the range of the average hammer price.

Therefore, an estimated maximum purchase price could be around 1000 euros. This is based on the demonstrated interest in previous auctions and the average hammer price, taking into account that the condition of the coin may influence the final price.