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 a medium-good quality. This suggests that its value should be in an intermediate range, but not at the highest level.

2. Auction History:
- The average hammer price in previous auctions is 294.47 euros.
- The coin has been auctioned 20 times, of which it has sold 17 times, indicating good demand.
- Previous hammer prices for coins with similar condition (75) have varied, but there are examples of auctions reaching up to 375 euros.

3. Starting Price and Estimates:
- The current starting price is 250 euros, which is a reasonable starting point.
- The estimated hammer price for this auction is 350 euros, suggesting that bidders are willing to pay more than the starting price.

4. Recent Trends: In the most recent auctions, hammer prices have been around 200-300 euros for similar conditions, but there are also examples of higher hammer prices.

Based on these factors, an estimated maximum purchase price could be around 350-400 euros, considering that the coin is in good condition and has shown a hammer price history that supports this figure. However, since the market can be volatile, it is advisable to keep an eye on the competition in the auction.