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

1. Current Grade: The coin has a grade of 80 (MS+). This is an important factor, as coins in better condition tend to reach higher prices.

2. Previous Auction Prices: By looking at previous auction prices for coins with similar grades, we can see that:
- In past auctions, coins with a grade of 80 have reached hammer prices of up to 111 euros.
- The average hammer price for coins of similar grade seems to be in the range of 80 to 100 euros.

3. Starting Price and Average Hammer Price: The current starting price is 50 euros, and the average hammer price in the past has been 94.04 euros. This suggests that the hammer price could be significantly higher than the starting price.

4. Recent Trends: In the most recent auctions, hammer prices have shown a trend of being in the range of 60 to 100 euros for similar grades.

Based on these points, an estimated maximum purchase price for this coin could be in the range of 90 to 110 euros. This is based on the current grade, previous hammer prices, and market trends. However, it is important to note that the final price may vary depending on competition in the auction and the interest of collectors.