To estimate a maximum purchase price for the coin with a grade of 70 (MS-), we can analyze historical data from previous auctions of coins with a similar grade and their hammer prices.

1. Historical Price Analysis:
- In the past, coins with a grade of 70 have had hammer prices that varied. For example:
- In a 2020 auction, a coin with a grade of 70 had a hammer price of 25 euros.
- In another 2020 auction, the hammer price was 31 euros.
- In 2021, the hammer price was 50 euros.
- In 2022, the hammer price was 70 euros.

2. Price Trends:
- Observing the hammer prices, it seems that coins with a grade of 70 tend to sell between 25 and 70 euros, with some peaks in specific auctions.

3. Starting Price and Average Price:
- The current starting price is 15 euros, and the average hammer price in the past has been 128.83 euros, but this includes coins of better grades.

4. Estimation:
- Given that the coin's grade is 70 (MS-), a reasonable hammer price could be in the range of 30 to 70 euros, based on previous auctions.

Conclusion:
An estimated maximum purchase price for this coin, considering its grade and historical prices, could be approximately 60 euros. This is based on the price trend for coins with a similar grade and the current market context.