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

1. Current Condition: The coin has a condition of 85 (MS+/EF-), which indicates that it is in quite good shape. This generally translates to a higher price compared to coins with lower conditions.

2. Starting Price and Average Hammer Price: The starting price is 600 euros, and the average hammer price in previous auctions is 695 euros. This suggests that the coin has a market value that could be above the starting price.

3. Auction History: By observing previous hammer prices for coins with similar conditions, we can see significant variations. For example, in past auctions, coins with conditions of 90 and 95 have sold for prices ranging from 840 to 2000 euros. However, there are also examples of coins with lower conditions that sold for less than 600 euros.

4. Price Trends: The general trend seems to be that coins with a condition of 85 can reach hammer prices around 800-1200 euros, depending on demand and other market factors.

Based on these points, an estimated maximum purchase price for this coin could be between 800 and 1000 euros, considering that the average hammer price is 695 euros and that the condition is relatively good. However, given the auction history and price variability, a maximum of 1000 euros seems reasonable if demand is high.