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

1. Coin Condition: The coin has a condition rating of 80 (MS+). This is an important factor, as coins in better condition tend to reach higher prices.

2. Previous Prices: By observing the hammer prices of coins with similar conditions, we can see that prices have varied. For example, in previous auctions, coins with conditions ranging from 80 to 90 have reached hammer prices between 270 and 400 euros.

3. Starting Price and Average Hammer Price: The current starting price is 400 euros, and the average hammer price in the past has been 266.85 euros. This suggests that the starting price is relatively high compared to the average hammer price.

4. Recent Trends: In the most recent auctions, hammer prices have shown an upward trend, especially for coins in good condition.

5. Comparison with Similar Auctions: In previous auctions, coins with condition ratings of 80 have reached hammer prices of up to 400 euros, especially if they were auctioned in a favorable context.

Taking all these factors into account, an estimated maximum purchase price for this coin could be around 450 euros. This price reflects a balance between the coin's condition, previous hammer prices, and the current market trend.