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

1. Current Condition: The coin has a condition of 70 (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 coins with a similar condition (70) in the past has been 55 euros (in the auction of 2020-12-15).
- In other auctions, hammer prices have varied, but the range seems to be between 20 and 120 euros, depending on the condition and demand.

3. Starting Price and Average Hammer Price:
- The current starting price is 40 euros, which is slightly higher than the average starting price of 30.7 euros.
- The average hammer price is 38.9 euros, suggesting that buyers are willing to pay a bit more than the starting price in general.

4. Recent Trends:
- In the most recent auctions, hammer prices have shown a trend of being higher, especially for coins in good condition.

Based on these factors, an estimated maximum purchase price could be in the range of 60 to 70 euros, considering that the condition is good and there is a history of hammer prices that supports this estimate.

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