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

1. Current Condition: The coin has a condition of 95 (S/C-), indicating that it is in very good shape. This generally translates to a higher price compared to coins in lower condition.

2. Previous Prices: By looking at previous auction prices for coins with a similar condition (95), we can see that they have reached auction prices that vary, but are generally in the range of 400 to 777 euros. For example:
- In 2020, a coin with a condition of 100 was auctioned for 440 euros.
- In 2019, a coin with a condition of 95 was auctioned for 400 euros.
- In 2021, a coin with a condition of 95 was auctioned for 420 euros.

3. Average Auction Price: The average auction price for this coin is 456.74 euros, which is also a good indicator of the expected value.

4. Starting Price: The current starting price is 350 euros, suggesting that the seller expects a reasonable price, but the final auction price could be significantly higher.

5. Auction Trends: The coin has been auctioned 27 times, of which 20 have sold. This indicates a consistent interest in the coin, which may increase its value.

Based on these factors, an estimated maximum purchase price could be in the range of 500 to 600 euros, considering that the condition is high and previous auction prices have reached similar figures. Therefore, a reasonable maximum purchase price could be 550 euros.