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

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

2. Current Starting Price and Previous Prices: The current starting price is 1400 euros. In previous auctions, hammer prices have varied, but there is a price pattern that can be observed:
- In 2022, a coin with a similar condition (85) was auctioned for 1405 euros with a starting price of 1200 euros.
- In 2018, a coin with a condition of 85 was auctioned for 900 euros with a starting price of 900 euros.
- In other auctions, hammer prices have ranged between 706 and 1100 euros for lower conditions.

3. Price Trends: The average hammer price in previous auctions is 963.22 euros, suggesting that the hammer price may be lower than the current starting price. However, since the coin has sold in all previous instances and considering the condition, it is reasonable to expect that the hammer price will be closer to the current starting price.

4. Sales Expectations: Given that the coin has sold in all previous instances and there is consistent demand, this may influence a higher hammer price.

Based on these factors, an estimated maximum purchase price could be in the range of 1300 to 1500 euros, considering that the starting price is 1400 euros and that the condition is good. This allows for some competition in the auction but also reflects the coin's value in the current market.

Therefore, an estimated maximum purchase price could be 1500 euros.