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

1. Starting Price: 250 euros. This is the initial price set for the auction.
2. Condition: The coin has a condition rating of 80 (MBC+), indicating that it is in quite good shape. Coins in this category usually have a higher value than those in lower conditions.
3. Auction History: The coin has been auctioned once in the past but did not sell. This may indicate that the interest in the coin was not sufficient to reach the starting price in the previous auction.
4. Average Hammer Price: There is no data on previous hammer prices, making it more difficult to establish a price range based on past auctions.

Given that the coin is in good condition (MBC+) and has a starting price of 250 euros, but did not sell in the previous auction, it is possible that market interest is not as high as expected.

Taking these factors into account, an estimated maximum purchase price could be set between the starting price and 20% above it, considering the good condition. This leads us to a range of:

- Estimated Maximum Purchase Price: 250 euros (starting price) + 50 euros (20% of 250) = 300 euros.

Therefore, a reasonable maximum purchase price could be 300 euros.