To estimate a maximum purchase price for the coin in question, we can analyze the provided data, including the current grade, previous auction prices, and trends in past auctions.

1. Current Grade: The coin has a grade of 70 (MBC-), indicating that it is in acceptable condition, but not of the highest quality.

2. Previous Auction Prices:
- In previous auctions, hammer prices have varied considerably. For example:
- In 2022, a coin with a grade of 75 sold for 170 euros.
- In 2023, a coin with a grade of 80 sold for 150 euros.
- In 2020, a coin with a grade of 70 sold for 40 euros.

3. Price Trends:
- The average hammer price for this coin is 73.89 euros, suggesting that, in general, buyers are willing to pay around this price.
- The average starting price is 29 euros, indicating that sellers are starting the auctions at a lower price.

4. Estimation Based on Grade:
- Given that the coin's grade is 70, and considering that in the past it has sold for prices around 35-40 euros in similar conditions, we can estimate that the hammer price could be in a similar range.

5. Maximum Purchase Price:
- Taking all these factors into account, an estimated maximum purchase price could be between 40 and 60 euros, considering that price trends may vary and that the grade is an important factor.

Therefore, an estimated maximum purchase price for this coin could be 50 euros.