To estimate a maximum purchase price for the coin in question, we can consider several factors based on the provided data:

1. Current Grade: The coin has a grade of 70 (MS-). This is an important factor, as coins in better condition tend to reach higher prices.

2. Historical Prices: By looking at previous auction prices for coins with similar grades, we can see that:
- In past auctions, coins with a grade of 70 have reached hammer prices of up to 114.38 euros (2016) and 95 euros (2022).
- The average hammer price for coins of similar grade seems to be in the range of 40 to 95 euros.

3. Starting Price and Average Hammer Price: The current starting price is 30 euros, and the average hammer price in the past has been 83.17 euros. This suggests that there is potential for an increase in the hammer price.

4. Recent Trends: In the most recent auctions, the hammer price has varied, but there have been examples of similar coins selling for higher prices, indicating that interest in these coins may be increasing.

Based on these factors, an estimated maximum purchase price for this coin could be in the range of 90 to 120 euros, considering that the grade is good and there is a history of hammer prices that supports this estimate. However, since the starting price is 30 euros, it is possible that buyers may be willing to bid more, especially if there is interest in the coin.

Therefore, a reasonable maximum purchase price could be 100 euros.