To estimate a maximum purchase price for the coin in question, we can analyze the provided data, especially the current grade of the coin (70, MS-) and the previous auction prices of coins with similar grades.

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

2. Previous Auction Prices: By observing the auction prices of coins with similar grades (70 and 75), we can see that:
- In previous auctions, coins with a grade of 70 have had hammer prices ranging from 28 to 55 euros.
- Coins with a grade of 75 have had hammer prices ranging from 30 to 85 euros.

3. Average Hammer Price: The average hammer price for this coin is 58 euros, which is also a good indicator of market value.

4. Recent Trends: In the most recent auctions, hammer prices have shown a trend of being in the range of 50 to 100 euros for grades from 70 to 80.

5. Starting Price: The starting price is 18 euros, which suggests that there is considerable room for the hammer price to be higher.

Based on these points, an estimated maximum purchase price for the coin, considering its grade and previous auction prices, could be in the range of 70 to 85 euros. This aligns with the hammer prices of coins of similar grade and the observed average hammer price.