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

1. Starting price: 350 euros.
2. Auction history: The coin has been auctioned 15 times, of which it has sold 10 times. This indicates a sell-through rate of 66.67%, which is quite positive.
3. Previous prices: Previous hammer prices for coins of similar condition (80) have varied, but the highest hammer price was 550 euros in March 2024. This suggests there is significant potential to reach high prices in recent auctions.
4. Average hammer price: The average hammer price of 292.3 euros is a good indicator of what buyers are willing to pay on average.
5. Condition: There is no information about the condition of this coin, which may make buyers more cautious. However, most coins in the history have a condition of 80, suggesting that the coin could be in a similar state.

Given that the starting price is 350 euros and considering the auction price history, an estimated maximum purchase price could be positioned between the starting price and the highest previous hammer price.

Taking all these factors into account, an estimated maximum purchase price could be approximately 450 euros. This reflects a balance between the starting price and the hammer price potential based on the auction history.