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

1. Current Condition: The coin has a condition of 75 (MBC), which indicates that it is in fairly good shape, but not the best possible condition.

2. Auction History:
- It has been auctioned 4 times in the past, of which it has sold 2 times and not sold 2 times. This suggests that there is interest in the coin, but also that there may be some resistance in the price.
- The average starting price in previous auctions is 113.33 euros, and the average hammer price is 85 euros. This indicates that, in general, buyers are willing to pay less than the starting price.

3. Previous Prices:
- In the auction of October 2022, the coin with a condition of 75 had an estimated price of 350 euros, but the hammer price is unknown. This suggests that the value of the coin may be high, but there may also be fluctuations in the market.
- In the auction of April 2022, a coin with a condition of 80 sold for 70 euros, indicating that condition significantly affects the price.

4. Current Starting Price: The starting price is 100 euros, which may be a good starting point for the auction.

Taking all these factors into account, an estimated maximum purchase price could be in a range between 85 and 120 euros, considering that the average hammer price is 85 euros and the average starting price is 113.33 euros.

Therefore, a reasonable maximum purchase price could be 120 euros, as it aligns with the estimated prices from previous auctions and the current condition of the coin.