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

1. Coin Condition: The coin has a condition rating of 75 (MS), indicating that it is in quite good shape. This generally translates to a higher price compared to coins with lower conditions.

2. Auction History: The coin has been auctioned 28 times, of which it has sold 26 times. This suggests there is consistent interest in this coin, which can increase its value.

3. Previous Prices: By looking at previous hammer prices for coins with a similar condition (75), we can see there is a price range. For example, at the auction on July 14, 2022, a coin with the same condition sold for 600 euros. However, there are also lower prices in other auctions.

4. Average Hammer Price: The average hammer price for this coin is 226.52 euros, which can serve as a reference point.

5. Starting Price: The starting price is 300 euros, indicating that the seller expects a reasonable price for the coin.

Taking all these factors into account, an estimated maximum purchase price could be in the range of 400 to 600 euros, considering that the condition is good and there have been previous sales in that range. However, since the starting price is 300 euros, it is likely that the hammer price will not significantly exceed this value unless there is strong competition in the auction.

Therefore, a reasonable maximum purchase price could be 500 euros.