To estimate a maximum purchase price for the coin in question, we can analyze the provided data, especially the previous auction prices and the current condition of the coin.

1. Condition of the coin: The coin has a condition rating of 80 (MS+), indicating that it is in fairly good shape, but not the best possible condition.

2. Previous auction prices: By looking at the auction prices of coins with a similar condition (80), we can see that they have varied, but generally, the auction prices have been in a range that may be indicative of the current value.

3. Average auction price: The average auction price for this coin is 556.76 euros, which gives us a good reference point.

4. Price trends: In previous auctions, the hammer prices for coins with a condition of 80 have ranged between 380 and 650 euros, depending on demand and other factors.

5. Starting price: The starting price is 300 euros, which is a good starting point.

Based on these factors, an estimated maximum purchase price could be around 600 euros, as this is a price that has been reached in previous auctions for coins in similar conditions and aligns with the average auction price. However, it is important to consider that the final price may vary depending on the competition in the auction and the interest of collectors at that time.