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

1. Current Condition: The coin has a condition of 70 (VF-), indicating that it is in fairly good shape, although not the best possible condition.

2. Auction History:
- In the past, this coin has been auctioned 3 times and has sold on all occasions.
- The average hammer price in previous auctions is 74 euros, suggesting that buyers are willing to pay a considerable price for this coin.

3. Previous Prices:
- In the November 2020 auction, the coin sold for 20 euros with a condition of 30.
- In the May 2024 auction, the same coin sold for 170 euros with a condition of 80. This indicates that the price can increase significantly with better condition.

4. Starting Price and Estimates:
- The current starting price is 25 euros, which is reasonable given the price history.
- The average hammer price of 74 euros suggests that there is much higher selling potential.

Given that the current condition of the coin is 70, which is better than the 30 in the 2020 auction but lower than the 80 in the 2024 auction, we can estimate that the hammer price could be in an intermediate range.

Estimated Maximum Purchase Price: Considering all these factors, a reasonable maximum purchase price could be between 80 and 100 euros, given the price history and current condition. This would allow for competitive bidding in the auction without exceeding the market value observed in previous auctions.