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 Starting Price and Previous Prices: The current starting price is 400 euros, and the average hammer price in previous auctions is 397.23 euros. This suggests that the starting price is aligned with the market value.

3. Sales History: The coin has been sold in 22 out of the last 26 auctions, indicating good demand. Additionally, the highest hammer price in the past was 620 euros (in 2014), which sets a precedent for a higher price.

4. Recent Trends: In the most recent auctions, hammer prices have ranged from 360 to 480 euros for coins with similar conditions.

5. Maximum Price Estimate: Given that the condition is good and considering the price history, a reasonable maximum purchase price could be in the range of 500 to 600 euros. This is based on the fact that the highest hammer price in the past was 620 euros and that the current starting price is 400 euros.

Therefore, an estimated maximum purchase price for this coin could be 550 euros. This allows for some margin for competition in the auction, given that there is interest in the coin and its condition is favorable.