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

1. Current Condition: The coin has a condition of 75 (MBC), which is a fairly good state. This suggests that its value should be in a medium-high range.

2. Auction History:
- The average hammer price from previous auctions is 399.29 euros, indicating that, in general, coins of this reference tend to sell for prices above their starting price.
- In previous auctions, hammer prices have varied, but there are examples of sales exceeding 500 euros, especially in similar conditions.

3. Current Starting Price: The starting price is 250 euros, which is reasonable given the history of hammer prices.

4. Price Trends: Looking at previous hammer prices, the highest recorded price was 650 euros in an auction with a condition of 80. This suggests that, although the current coin's condition is slightly lower, it could still reach a significant price.

5. Estimation: Given that the average hammer price is 399.29 euros and considering that the condition is 75, an estimated maximum purchase price could be between 400 and 500 euros, taking into account that the market can be competitive and there is a history of high prices.

Therefore, an estimated maximum purchase price for this coin could be approximately 450 euros.