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

1. Current Condition: The coin has a condition of 70 (MBC-), indicating that it is in relatively good shape. This suggests that its value should be above that of coins in worse conditions.

2. Auction History:
- The average hammer price for similar coins in the past is 89.4 euros, indicating significant interest in this coin.
- In previous auctions, hammer prices have varied, but there are examples of coins with similar conditions that have sold for prices ranging from 15 to 60 euros.

3. Starting Price and Average Starting Price:
- The current starting price is 25 euros, which is a reasonable starting point.
- The average starting price of 29.09 euros also suggests that this is an acceptable range to begin with.

4. Sales Trends: Since this coin has sold every time it has been auctioned, this indicates consistent demand.

5. Maximum Price Estimate:
- Considering the average hammer price of 89.4 euros and the fact that the condition is 70, a maximum purchase price could be set in a range that reflects both demand and condition.
- A conservative approach could be to set a maximum purchase price around 70-80 euros, as this aligns with the hammer price history and current condition.

Therefore, an estimated maximum purchase price for this coin could be 80 euros.