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

1. Current Condition: The coin has a grade of 70 (MS-). This indicates that it is in an acceptable state, but it is not of the highest quality.

2. Historical Prices: By looking at previous auction prices for coins with a similar grade (70), we can see that the hammer price has varied. For example:
- In a 2020 auction, a coin with a grade of 70 sold for 18 euros.
- In another auction in 2023, a coin with a grade of 70 sold for 20 euros.

3. Average Hammer Price: The average hammer price for this coin is 114.55 euros, but this may be influenced by coins in better condition or by exceptional auctions.

4. Current and Average Starting Price: The current starting price is 15 euros, and the average starting price is 59.77 euros. This suggests that the market has higher expectations than the starting price.

5. Recent Trends: In the most recent auctions, hammer prices for coins with a grade of 70 have been in the range of 20 to 25 euros.

Based on these factors, an estimated maximum purchase price for the coin in question could be between 25 and 30 euros. This is based on recent price trends and the condition of the coin. However, since the market can be volatile, it is advisable to keep an eye on the auction and adjust the bid according to the competition.