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

1. Current Condition: The coin has a condition 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 Auction Prices: By looking at previous auction prices for coins with a similar condition (80), we can see that the auction prices have varied. For example, in past auctions, coins with a condition of 80 have reached hammer prices of up to 35-45 euros.

3. Average Hammer Price: The average hammer price for this coin is 47.87 euros, which is also a good indicator of the expected value.

4. Recent Trends: In the most recent auctions, hammer prices have shown an upward trend, especially for coins in good condition.

5. Starting Price and Average Starting Price: The current starting price is 18 euros, and the average starting price is 30.93 euros. This suggests that the starting price is below average, which could indicate a good buying opportunity.

Taking all these factors into account, an estimated maximum purchase price for this coin could be between 45 and 60 euros, considering that the condition is good and there is an upward trend in hammer prices. However, to be more conservative, a maximum purchase price of 50 euros could be a reasonable option.