To estimate a maximum purchase price for the coin in question, let's consider several factors:

1. Starting Price: 250 euros. This is the initial price of the auction.
2. Condition: The coin has a condition rating of 80 (MBC+), indicating that it is in quite good shape. This can positively influence its value.
3. Auction History: The coin has been auctioned 2 times in the past, of which it has sold once. This suggests that there is interest in the coin, although it also indicates that it does not always sell.
4. Previous Prices: In the October 2022 auction, the starting price was 300 euros, with an estimated price of 400 euros. This suggests that the perceived value of the coin may be higher than the current starting price.
5. Average Hammer Price: The average hammer price in previous auctions was 262 euros, which can serve as a reference for the actual value of the coin.

Given that the starting price is 250 euros and considering the auction history and the condition of the coin, an estimated maximum purchase price could be positioned between the average hammer price and the previous estimated price.

Therefore, a reasonable maximum purchase price could be around 350 euros. This takes into account the interest in the coin, its good condition, and the price history in previous auctions.