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

1. Coin Condition: The coin to be auctioned 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. Price History: By looking at previous auction prices for coins with a similar condition (95), we can see that they have reached auction prices of up to 220 euros (in December 2020) and other lower prices in past auctions. However, the most recent auction price for a coin with a condition of 95 was 18 euros in May 2023.

3. Average Auction Price: The average auction price for this coin is 42.18 euros, which is also an important indicator.

4. Starting Price and Estimated Prices: The current starting price is 12 euros, and the average starting price in the past has been 17.2 euros. This suggests that the starting price is reasonable and could attract bidders.

Taking all these factors into account, an estimated maximum purchase price could be in the range of 50 to 100 euros, considering that the condition is high and there are precedents of higher auction prices in the past. However, given the most recent auction price of 18 euros, it is wise not to exceed 100 euros in the bid.

Therefore, an estimated maximum purchase price could be 80 euros.