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

1. Current Condition: The coin has a condition rating of 80 (MBC+), indicating that it is in quite good shape. This generally translates to a higher price compared to coins with lower conditions.

2. Current Listing Price and Previous Prices: The current listing price is 600 euros, which is significantly higher than the average listing price of 278.76 euros. However, the average hammer price is 412.26 euros, suggesting that the market has been willing to pay less than the current listing price in previous auctions.

3. Sales History: The coin has sold in 4 out of the last 6 auctions, indicating a consistent interest in the coin. However, it should also be noted that there have been 2 occasions when it did not sell.

4. Previous Hammer Prices: Previous hammer prices varied, but the highest was 1100 euros in a recent auction with a condition of 95. This suggests that the price could increase significantly with better condition.

5. Price Trends: Observing previous hammer prices, the price has been increasing, especially in the more recent auctions. This could indicate an upward trend in interest for this coin.

Considering all these factors, an estimated maximum purchase price could be in the range of 600 to 800 euros, given that the listing price is 600 euros and the condition is good, but not exceptional. A price of 800 euros could be a reasonable limit, given the price history and current condition.