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

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

2. Historical Prices: By looking at the auction prices of coins with similar conditions (around 80), we can see that the final prices have varied. For example:
- In previous auctions, coins with a condition of 80 have reached final prices between 40 and 90 euros.
- The average final price for coins with similar conditions seems to be around 50-60 euros.

3. Starting Price and Average Final Price: The current starting price is 25 euros, and the average final price in the past has been 52.95 euros. This suggests that the market is willing to pay more than the starting price.

4. Recent Trends: In the most recent auctions, final prices for coins with similar conditions have shown an increase, which could indicate a rising trend in interest for these coins.

Based on these factors, an estimated maximum purchase price for this coin could be between 60 and 80 euros, considering that the condition is good and that market interest seems to be increasing.

Therefore, a reasonable maximum purchase price could be 70 euros.