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 85 (MS+/EF-), indicating that it is in quite good shape. This generally translates to a higher price compared to coins of lower condition.

2. Current Listing Price and Previous Prices: The current listing price is 750 euros. In previous auctions, the hammer price has varied, but there are examples of hammer prices exceeding 1000 euros for coins in similar or better conditions.

3. Historical Trends: By observing the hammer prices of coins with similar conditions (around 85), we can see that they have reached hammer prices of up to 1200 euros in the past. However, there are also examples of lower prices, suggesting that the market can be variable.

4. Average Hammer Price: The average hammer price for similar coins is approximately 605.06 euros, indicating that the hammer price may be below the current listing price.

5. Demand and Supply: The coin has been auctioned 57 times, with a sell-through rate of 93% (53 out of 57). This suggests that there is consistent interest in this coin, which could push the price upward.

Taking all these factors into account, an estimated maximum purchase price could be between 900 and 1100 euros. This is based on the condition of the coin, previous hammer prices, and market trends. A price of 1000 euros could be a reasonable target, given that it has been reached in previous auctions for coins in similar conditions.