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. Historical Prices: By looking at previous auction prices for coins with similar conditions, we can see that:
- In 2018, a coin with a condition of 70 was auctioned for 30 euros.
- In 2021, a coin with a condition of 80 was auctioned for 65 euros.
- In 2022, a coin with a condition of 80 was auctioned for 85 euros.

3. Average Auction Price: The average auction price for this coin is 43.43 euros, which also gives us a reference.

4. Auction Trends: The coin has been auctioned 18 times, of which 15 have sold. This indicates a consistent interest in the coin, which may influence its price.

5. Starting Price and Average Starting Price: The starting price is 18 euros, and the average starting price is 38.37 euros. This suggests that the starting price may be below the actual value of the coin.

Taking all these factors into account, an estimated maximum purchase price for the coin could be between 50 and 70 euros, considering that the condition is good and there is a price history that supports this estimate. However, since the condition is 70, a more conservative price could be around 50 euros.