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

1. 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 with lower conditions.

2. Auction History:
- The average hammer price for this coin in the past is 549.6 euros.
- In recent auctions, the hammer price has varied, but it has reached significantly higher figures, such as 3200 euros in a 2022 auction.
- The last auction with a starting price of 400 euros had a hammer price of 550 euros.

3. Price Trends:
- The current starting price is 400 euros, which is slightly higher than the average starting price of 258.09 euros, suggesting an expectation that the coin may reach a higher price.
- Given that there have been auctions where the hammer price exceeded 1000 euros, it is reasonable to consider that interest in this coin may be high.

4. Comparison with Previous Prices:
- In previous auctions with similar conditions, hammer prices have ranged from 220 to 3200 euros, showing a wide variability.

Based on these factors, an estimated maximum purchase price could be in the range of 600 to 800 euros, considering that the coin is in good condition and there is a history of hammer prices suggesting significant interest. However, given the history of high prices, a maximum price of up to 1000 euros could be considered if there is strong competition in the auction.