To estimate a maximum purchase price for the coin in question, we can consider several factors based on the provided data:

1. Current Condition: The coin has a condition rating of 75 (MBC), indicating that it is in an acceptable state, but not among the best conditions.

2. Auction History:
- The average hammer price for this coin has been 431.95 euros.
- In previous auctions, hammer prices have varied, with some reaching up to 850 euros in a recent auction (2023-03-16) for a coin with a condition rating of 85.
- Most coins with a similar condition (75) have had hammer prices ranging between 220 and 420 euros.

3. Starting Price: The current starting price is 250 euros, which may be a good indicator of initial interest in the coin.

4. Price Trends: Observing the hammer prices of coins with similar conditions, it seems that the hammer price range for coins in MBC condition (75) is between 220 and 360 euros.

Based on these factors, an estimated maximum purchase price for the coin could be around 400 euros. This is because, although the condition is not the highest, the interest in the coin and the price history suggest that it could reach a competitive price at auction.