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

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

2. Previous Prices:
- In the 2020 auction, the coin sold for 6 euros with a condition of 90.
- In the 2014 auction, the final price was 9 euros, although the condition is not specified.

3. Starting Prices and Average Prices:
- The current starting price is 18 euros, which is significantly higher than previous final prices.
- The average starting price is 11 euros, and the average final price is 7.5 euros.

4. Supply and Demand: The coin has been auctioned twice in the past and sold both times, indicating interest in the coin.

Given that the current condition is better than previous ones and considering the starting price, an estimated maximum purchase price could be between the starting price and the previous average final price.

Taking all these factors into account, an estimated maximum purchase price could be approximately 12 to 15 euros. This reflects interest in the coin, its good condition, and the price history, without reaching the current starting price, which may be a bit high compared to previous final prices.