To estimate a maximum purchase price for the coin in question, we will 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 coins with similar condition (70) in the past has been approximately 30-40 euros.
- In previous auctions, coins with a condition of 70 have reached hammer prices that varied, but generally fall within the range of 22 to 30 euros.

3. Starting Price and Average Hammer Price:
- The current starting price is 18 euros, which is relatively low compared to the average hammer price of 58.45 euros.
- The average starting price of 40.09 euros also suggests that there is potential for an increase in the hammer price.

4. Recent Trends: In the most recent auctions, the hammer price for coins with a condition of 70 has been around 30-40 euros, indicating that interest in these coins remains strong.

Based on these factors, an estimated maximum purchase price for this coin could be between 40 and 50 euros. This is based on the historical hammer prices for coins of similar condition and the potential increase in collector interest.