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 of high quality. This may influence the price, as coins in better condition tend to reach higher prices.

2. Previous Prices: By observing previous auction prices for coins with similar conditions, we can see that the hammer prices for coins with a condition of 75 have varied. For example, in previous auctions, coins with a condition of 75 have reached hammer prices of around 304 euros.

3. Starting Price and Average Hammer Price: The current starting price is 400 euros, which is higher than the average hammer price of 323.88 euros. This suggests that the starting price may be a bit optimistic, given the price history.

4. Recent Trends: In the most recent auctions, hammer prices for coins of similar condition have shown a range that can go from 300 to 400 euros, depending on demand and other market factors.

Based on these points, an estimated maximum purchase price for this coin could be around 350-375 euros. This is based on the analysis of previous prices and the current condition, suggesting that a hammer price in this range would be reasonable, considering that the starting price is 400 euros.