To estimate a maximum purchase price for the coin in question, we will 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 Auction Prices: By looking at the hammer prices of coins with a similar condition (80) in the past, we can see that the hammer prices have varied. For example, in previous auctions, coins with a condition of 80 have reached hammer prices of up to 170 euros.

3. Average Hammer Price: The average hammer price for this coin is 128.83 euros, which provides a good reference for the expected value.

4. Starting Price and Average Starting Price: The current starting price is 50 euros, and the average starting price is 81.02 euros. This suggests that the market is willing to pay more than the starting price.

5. Recent Trends: The price trend in recent auctions is also important. If similar coins have been increasing in price, this could indicate a rise in demand.

Based on these factors, an estimated maximum purchase price for this coin could be in the range of 150 to 200 euros, considering that the condition is good and there are precedents of higher hammer prices in the past.

Therefore, a reasonable maximum purchase price could be 180 euros.