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

1. Current 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. Auction History:
- The average hammer price for this coin is 77.5 euros, suggesting that, in general, buyers are willing to pay close to this price.
- In previous auctions, we have seen hammer prices that varied significantly, but there are examples of coins in similar conditions that have sold for higher prices, such as 190 euros for a coin with a condition of 95.

3. Starting Price and Previous Prices:
- The current starting price is 25 euros, which is relatively low compared to the average hammer price.
- In recent auctions, coins with similar conditions have reached hammer prices of 55 euros (in a 2022 auction) and 35 euros (in a 2023 auction).

4. Sales Trends: The coin has sold in 76.9% of past auctions (20 out of 26), indicating a consistent interest in the coin.

Based on these factors, an estimated maximum purchase price could be in the range of 70 to 90 euros, considering that the condition is good and the price history suggests that buyers are willing to pay more than the starting price. A price of 80 euros could be a reasonable target, as it aligns with the average hammer price and the condition of the coin.