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

1. Current Condition: The coin has a condition rating 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. Current Listing Price and Previous Prices: The current listing price is 90 euros. In previous auctions, we have seen hammer prices that varied significantly, but there are examples of coins with similar conditions that have sold for higher prices. For instance, in 2018, a coin with a condition of 80 sold for 55 euros, and in 2021, another with a condition of 80 sold for 95 euros.

3. Sales Trends: The coin has been auctioned 67 times, of which 58 resulted in sales. This indicates a consistent interest in the coin, which may increase its value.

4. Average Hammer Price: The average hammer price for this coin is 83.88 euros, suggesting that the listing price of 90 euros is in line with market expectations.

5. Proximity of Future Auctions: There are 2 auctions scheduled in the coming days, which may influence demand and price.

Taking all these factors into account, an estimated maximum purchase price could be around 110-120 euros. This is based on the coin's condition, market interest, and previous hammer prices for coins of similar condition. However, it is important to remember that the final price may vary depending on competition in the auction and other market factors at the time of sale.