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 the same grade and similar characteristics.

1. Historical Data:
- In the past, coins with a grade of 70 have had varying auction prices. For example:
- In 2020, a coin with a grade of 70 was auctioned for 65 euros.
- In 2018, another coin with the same grade sold for 50 euros.
- In 2022, a coin with a grade of 70 was auctioned for 160 euros, but this may be an exceptional case.

2. Average Auction Price:
- The average auction price for similar coins has been approximately 83.79 euros.

3. Recent Trends:
- In recent auctions, the auction prices for coins with a grade of 70 have shown a range from 50 to 160 euros, depending on demand and other factors.

4. Estimation:
- Given that the coin's grade is 70 and considering the average auction price and previous auction prices, an estimated maximum purchase price could be in the range of 80 to 100 euros. This is based on the trend of auction prices and the coin's grade.

Therefore, an estimated maximum purchase price for this coin could be 100 euros.