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

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

2. Auction History:
- The average hammer price for similar coins in condition 70 has been approximately 51.97 euros.
- In previous auctions, coins with a condition of 70 have reached hammer prices of up to 65 euros (as seen in the auction on September 19, 2019).

3. Starting Price and Average Starting Price:
- The current starting price is 18 euros, which is relatively low compared to the average hammer price.
- The average starting price of 31.13 euros also suggests that there is potential for an increase in the hammer price.

4. Recent Trends: In the most recent auctions, hammer prices for coins of similar condition have varied, but they have generally remained in a range that suggests interest in these coins remains strong.

Based on these factors, an estimated maximum purchase price for this coin could be between 60 and 70 euros, considering that the interest in the coin and its condition are favorable. This aligns with previous hammer prices and the coin's potential in the current market.