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

1. Condition: The coin has a condition rating of 95 (S/C-), indicating that it is in very good shape. This generally increases its value compared to coins with lower conditions.

2. Auction history:
- The average hammer price for coins with a similar condition (95) has been between 20 to 25 euros in several previous auctions.
- In the most recent auction, a coin with the same condition sold for 120 euros, indicating a potential for high demand.

3. Starting price and previous prices:
- The current starting price is 18 euros, which is reasonable given the history of starting and hammer prices.
- The average hammer price in the past has been 24.42 euros, suggesting that the hammer price could be in a similar range.

4. Auction trends: The coin has been auctioned 17 times, of which 12 have sold. This indicates a consistent interest in the coin, which may influence the price.

Based on these factors, an estimated maximum purchase price could be between 25 and 30 euros, considering that the condition is high and there is a price history that supports this estimate. However, given the interest in the coin and the highest recorded hammer price, a maximum purchase price of up to 35 euros could be reasonable if one seeks to secure the acquisition.