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

1. Current Condition: The coin has a condition of 80 (MBC+), which indicates that it is in quite good shape. This generally translates to a higher price compared to coins in lower condition.

2. Auction History:
- In the past, the coin has been auctioned 6 times, of which it has sold 4 times. This suggests that there is consistent interest in the coin.
- Previous hammer prices are relevant. For example:
- In 2020, it sold for 800 euros with a condition of 80.
- In 2020, with a condition of 85, it sold for 950 euros.
- In 2019, with a condition of 75, it sold for 500 euros.
- In 2022, with a condition of 80, it did not sell, but the starting price was 350 euros.
- In 2024, with a condition of 85, the starting price was 500 euros.

3. Starting Price and Average Hammer Price:
- The current starting price is 800 euros, which is consistent with previous starting prices.
- The average hammer price is 775 euros, indicating that, in general, coins of this reference tend to sell close to this price.

4. Estimation Based on Condition and Previous Prices:
- Given that the coin's condition is 80, and considering that it has sold for 800 euros in similar conditions in the past, an estimated maximum purchase price could be in the range of 800 to 950 euros, depending on the competition in the auction and the interest from collectors.

Conclusion: Based on the previous analysis, an estimated maximum purchase price for this coin could be approximately 900 euros. This takes into account the condition, price history, and interest in the coin.