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. Auction History:
- The coin has been auctioned 13 times, of which it has sold 11 times. This suggests there is consistent interest in the coin.
- The average hammer price in the past is 485.67 euros, which can serve as a good indicator of market value.

3. Starting and Hammer Prices:
- The current starting price is 400 euros. In previous auctions, starting prices have varied, but the hammer price has often exceeded the starting price, especially for similar conditions (80).
- For example, in the auction on 2022-05-23, the starting price was 220 euros and the hammer price was 600 euros, indicating that there is potential for the hammer price to be significantly higher than the starting price.

4. Price Trends:
- In recent auctions, hammer prices have been in a range that suggests the coin could reach higher prices, especially considering that the average hammer price is 485.67 euros.

Based on these factors, an estimated maximum purchase price could be in the range of 600 to 700 euros, as this aligns with previous hammer prices and the good condition of the coin. However, it is important to keep in mind that the final price may vary depending on competition in the auction and the interest of other buyers.