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 approximately 37.8 euros.
- In previous auctions, hammer prices for coins with a condition of 95 have varied, but some have reached up to 120 euros in exceptional conditions.

3. Starting price and previous prices:
- The current starting price is 18 euros, which is relatively low compared to previous hammer prices.
- The average starting price in the past has been 24.47 euros, suggesting that the current starting price could be attractive to buyers.

4. Sales trends: The coin has been auctioned 30 times, of which 20 have sold, indicating good demand. Additionally, there has been a significant number of recent auctions with hammer prices ranging from 25 to 45 euros.

Based on these factors, an estimated maximum purchase price could be between 40 and 60 euros, considering that the condition is high and there is a history of hammer prices supporting this estimate. However, since the market can fluctuate, it is advisable to keep an eye on the auction and adjust the bid accordingly.