To estimate a maximum purchase price for the coin in question, we can analyze the provided data:

1. Condition: The coin has a condition rating of 95 (S/C-), indicating that it is in very good shape. This is relevant because coins in better condition tend to fetch higher prices at auctions.

2. Previous auction prices:
- The average hammer price at previous auctions for coins with a similar condition (95) has been approximately 513.79 euros.
- The hammer prices at previous auctions for this same reference have varied, but many have been in the range of 460 to 600 euros.

3. Current starting price: The starting price is 300 euros, which is relatively low compared to previous hammer prices.

4. Sales trends: The coin has been auctioned 25 times, of which 19 have sold. This indicates good demand, which can influence the hammer price.

5. Price estimates: The estimated price for the current auction is 500 euros, which also aligns with previous hammer prices.

Based on these factors, an estimated maximum purchase price could be in the range of 500 to 600 euros, considering that the starting price is 300 euros and that the condition is high. Therefore, a reasonable maximum purchase price could be 550 euros.