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 75 (MBC), which indicates that it is in an acceptable state, but not in the best condition.

2. Historical Prices: By looking at previous auction prices for coins with similar conditions (75 and 80), we can see that auction prices have varied, but generally have remained in a range of 260 to 360 euros.

3. Starting Price and Average Hammer Price: The current starting price is 400 euros, which is higher than the average hammer price of 299.08 euros. This suggests that the starting price may be a bit optimistic, given the sales history.

4. Recent Trends: In the most recent auctions, hammer prices for coins of similar condition have been around 360 euros, indicating that there is interest in this price range.

Based on these factors, an estimated maximum purchase price could be around 350-370 euros. This is based on the analysis of previous hammer prices and the current condition of the coin.