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

1. Starting Price: 300 euros. This is the initial price set for the auction.
2. Condition: The coin has a condition rating of 75 (MBC), indicating that it is in fairly good shape, although not the best possible condition.
3. Historical Data:
- In a previous auction, the same coin with a condition rating of 85 sold for 600 euros. This suggests that the price can vary significantly with the condition.
- The average hammer price for this coin in the past has been 600 euros, indicating that there is considerable interest in this coin.
4. Number of Auctions: It has been auctioned 2 times in the past, of which it sold 1 time. This suggests that there is an active market for this coin, although it is not extremely frequent.

Given that the current condition is lower than that of the previous auction that reached 600 euros, and considering the starting price of 300 euros, an estimated maximum purchase price could be in a range between the starting price and the average hammer price, adjusted for the condition.

Taking all these factors into account, an estimated maximum purchase price could be around 450-500 euros. This reflects interest in the coin, but also takes into account the lower condition compared to the previous auction.