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 70 (MS-). This is an important factor, as coins in better condition tend to reach higher prices.

2. Previous Auction Prices: By observing the hammer prices of coins with similar grades (70-80), we can see that:
- In 2018, a coin with a grade of 70 was auctioned for 31 euros.
- In 2019, a coin with a grade of 75 was auctioned for 75 euros.
- In 2018, another coin with a grade of 80 was auctioned for 45 euros.

3. Average Hammer Price: The average hammer price for this coin is 58 euros, indicating that, in general, coins of this reference tend to sell above their starting price.

4. Starting Price and Average Starting Price: The current starting price is 25 euros, and the average starting price is 41.78 euros. This suggests that the starting price is relatively low compared to the average hammer price.

5. Recent Trends: The coin has been auctioned 31 times in the past, with a sell-through rate of 93.5% (29 out of 31). This indicates consistent demand.

Based on these factors, an estimated maximum purchase price could be between 70 and 90 euros, considering that the grade is good and there are precedents for auctions in that range. However, since the starting price is 25 euros, it is likely that the hammer price will not significantly exceed the average hammer price of 58 euros.

Therefore, a reasonable estimated maximum purchase price could be 80 euros.