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

2. Auction History:
- The average hammer price in previous auctions is 56.38 euros.
- The coin has been auctioned 9 times, of which it has sold 8 times, indicating good demand.
- Previous hammer prices varied, but there are examples of hammer prices reaching up to 55 euros in similar conditions.

3. Starting Price and Average Starting Price:
- The current starting price is 50 euros, which is slightly lower than the average starting price of 53.67 euros. This may indicate that the seller is looking for a quick sale or that there is an expectation that the price will not rise much further.

4. Price Trends:
- In previous auctions, hammer prices have fluctuated, but there is a price pattern suggesting that coins in similar conditions have reached hammer prices ranging from 30 to 55 euros.

Based on these factors, an estimated maximum purchase price could be in the range of 60 to 70 euros. This is because, although the starting price is 50 euros, the good condition and price history suggest that there may be enough interest for the hammer price to exceed the previous average.

Therefore, a reasonable maximum purchase price could be 70 euros.