To estimate a maximum purchase price for the coin that is going to be auctioned, we can consider several factors based on the provided data:

1. Condition of the coin: The coin in question has a condition rating of 80 (MBC+), which indicates that it is in relatively good shape. This is important because coins in better condition tend to fetch higher prices.

2. Previous prices: By looking at the hammer prices of coins with similar conditions (around 80), we can see that the hammer prices have varied, but there are examples of auctions reaching up to 420 euros for coins with conditions of 95. For condition ratings of 80, hammer prices have been in the range of 240 to 320 euros.

3. Average hammer price: The average hammer price for this coin is 288.64 euros, which gives us a good reference for what buyers are willing to pay.

4. Starting price: The starting price is 300 euros, indicating that the auctioneer expects significant interest in the coin.

5. Auction trends: Given that there have been 76 previous auctions and 73 sales, this suggests that there is an active market for this coin.

Based on these factors, an estimated maximum purchase price could be in the range of 350 to 400 euros. This is because, although the starting price is 300 euros, the condition of the coin and market interest could lead to a higher hammer price, especially if there is competition among bidders.

Therefore, an estimated maximum purchase price could be 400 euros.