To estimate a maximum purchase price for the coin in question, we can analyze the provided data:

1. Current condition: The coin has a condition of 70 (MBC-). This indicates that it is in relatively good shape, but it is not the best possible condition.

2. Previous prices:
- The average hammer price for coins of similar condition (70) in previous auctions is 50 euros (in the January 2023 auction).
- In other auctions, we have seen hammer prices that vary, but the range seems to be between 41 and 150 euros for conditions of 70 and above.

3. Average hammer price: The average hammer price for this particular coin is 94.35 euros, suggesting that, in general, buyers are willing to pay close to this amount.

4. Auction trends: The coin has been auctioned 17 times and has sold every time, indicating consistent demand.

5. Comparison with starting and estimated prices: The current starting price is 25 euros, and the average starting price in the past has been 39.56 euros. This suggests that the current starting price is relatively low compared to the average hammer price.

Based on this data, an estimated maximum purchase price could be in the range of 90 to 120 euros, considering that the condition is good and the average hammer price is 94.35 euros. However, since the condition is not the highest, a more conservative price could be around 100 euros.

Therefore, a reasonable estimated maximum purchase price would be 100 euros.