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

1. Current Condition: The coin has a grade of 70 (MS-), indicating that it is in relatively good condition, but not among the highest quality.

2. Auction History:
- The average hammer price in previous auctions is 55.93 euros.
- The coin has been auctioned 15 times, of which it has sold 14 times, indicating good demand.
- In recent auctions, hammer prices have varied, but there are examples of sales in the range of 65 to 100 euros for coins with similar grades.

3. Starting and Hammer Prices:
- The current starting price is 25 euros, which is quite low compared to the average hammer price.
- In previous auctions, hammer prices for coins with similar grades have reached up to 100 euros.

4. Recent Trends: In the most recent auctions, hammer prices have been higher, especially for coins with grades of 80 or more.

Based on these factors, an estimated maximum purchase price could be in the range of 70 to 90 euros, considering that the coin's grade is 70 and there has been interest in similar coins in the past.

Therefore, a reasonable maximum purchase price could be 85 euros.