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

1. Current Condition: The coin has a condition of 70 (MS-). This indicates that it is in an acceptable state, but not of high quality.

2. Historical Prices: Looking at previous auction prices for coins with a similar condition (70), we find that:
- In several auctions, the hammer prices for coins with a condition of 70 have ranged between 15 and 30 euros.
- In previous auctions, the highest hammer price for a coin with a condition of 70 was 30 euros.

3. Average Hammer Price: The average hammer price for this coin is 80.88 euros, but this may be influenced by coins in better condition.

4. Starting Price: The current starting price is 18 euros, which suggests that the seller expects a lower price initially.

5. Auction Trends: Given that it has been auctioned 112 times and sold 97 times, there is good demand for this coin, which may increase its value.

Based on these factors, an estimated maximum purchase price for the coin with a condition of 70 could be between 30 and 40 euros, considering that it is a reasonable price given its state and historical prices. However, if there is strong competition in the auction, the price could exceed 40 euros.

Therefore, a reasonable maximum purchase price could be 40 euros.