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

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

2. Previous Prices: By looking at previous auction prices for coins with a similar condition (80), we can see that auction prices have varied, but have reached up to 130 euros in the case of a previous auction. However, most auction prices for similar conditions have been in the range of 50 to 90 euros.

3. Average Auction Price: The average auction price for this coin is 51.91 euros, which can also serve as a reference.

4. Starting Price: The current starting price is 40 euros, suggesting that the auctioneer expects moderate interest in the coin.

5. Auction Trends: The coin has been auctioned 61 times, of which 53 have been sold. This indicates good demand in the market.

Taking all these factors into account, an estimated maximum purchase price could be in the range of 80 to 100 euros. This is based on the coin's condition, previous auction prices, and general interest in the coin. Therefore, a reasonable maximum purchase price could be 90 euros.