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

1. Condition: The coin has a condition rating of 80 (MS+), indicating that it is in quite good shape. This generally translates to a higher price compared to coins with lower conditions.

2. Previous Prices:
- In past auctions, hammer prices have varied. For example, in 2014, a similar coin sold for 360 euros, indicating that there is a market willing to pay high prices for coins in good condition.
- The average hammer price of 240 euros is also a good indicator of market value.

3. Starting Price and Estimates: The current starting price is 200 euros, which is reasonable given the previous average hammer price. However, the estimated price of 250 euros suggests that there is potential for a higher hammer price.

4. Auction Trends: Given that there have been 5 previous auctions and 4 of them resulted in sales, this indicates a consistent interest in the coin. The only time it did not sell could be an isolated case.

5. Comparison with Previous Prices: The last auction had a starting price of 225 euros and an estimated price of 300 euros, suggesting that the market is willing to pay more for coins in similar conditions.

Taking all these factors into account, an estimated maximum purchase price could be around 300 euros, as this is a price that has been estimated in previous auctions and aligns with market interest. However, it is important to consider that the final price may vary depending on competition in the auction and demand at the time.