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

1. Current 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 in lower condition.

2. Auction History:
- The average hammer price in previous auctions is 17.67 euros.
- In past auctions, the hammer price has varied, with some prices reaching up to 35 euros under similar conditions.

3. Starting Price and Estimated Price:
- The current starting price is 12 euros, and the estimated price is 20 euros. This suggests that there are expectations for the coin to sell for a price higher than the starting price.

4. Sales Trends: Of the 19 times it has been auctioned, it has sold 12 times, indicating good demand.

5. Comparison with Previous Prices:
- In previous auctions with similar condition (95), the hammer prices have been 24 euros and 20 euros, suggesting that the market is willing to pay higher prices for coins in good condition.

Based on these factors, an estimated maximum purchase price could be between 25 and 30 euros, considering that the condition is high and that the hammer price history supports this estimate. Therefore, a reasonable maximum purchase price could be 30 euros.