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

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

2. Previous Prices: By looking at previous auction prices for coins with a similar condition (80), we can see that they have reached auction prices of up to 90 euros in the past. For example, at the auction on December 15, 2020, a coin with a condition of 80 was sold for 35 euros, and in other auctions, prices have varied but have reached up to 90 euros for higher conditions.

3. Average Auction Price: The average auction price for this coin is 65.02 euros, which can also serve as a reference.

4. Starting Price: The current starting price is 12 euros, suggesting that there is considerable room for the final auction price to be higher.

5. Market Trends: Since the coin has been auctioned 56 times and has had a high sales percentage (48 out of 56), this indicates a consistent interest in this coin, which may influence a higher auction price.

Based on these factors, an estimated maximum purchase price could be in the range of 80 to 100 euros. This is based on the current condition, previous auction prices, and general interest in the coin. However, it is important to note that the final price may vary depending on competition at the auction and other market factors at the time of the auction.