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

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

2. Auction History:
- The average hammer price for this coin in the past is 829.44 euros, suggesting that buyers are willing to pay significantly more than the starting price on many occasions.
- The last auction with a similar condition (80) had a hammer price of 395 euros in 2014, and 700 euros in 2022, indicating that interest and value for the coin have fluctuated, but tend to be higher in better conditions.

3. Starting Price and Average Hammer Price:
- The current starting price is 500 euros, which is reasonable given the price history. However, the average hammer price suggests that it could reach a higher price.

4. Market Trends: Given that the coin has been auctioned 16 times and all have sold, this indicates a consistent interest in the coin, which may increase its value.

Based on these factors, an estimated maximum purchase price could be in the range of 900 to 1100 euros, considering that the average hammer price has been 829.44 euros and that the current condition is quite good. This also takes into account the possibility that buyers may be willing to pay a bit more for a coin in good condition.

Therefore, an estimated maximum purchase price could be 1000 euros.