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

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

2. Auction History:
- The average hammer price for this coin in the past is 242 euros.
- In previous auctions, hammer prices have varied, with a maximum of 900 euros in a recent auction, although this may be an exceptional case.
- Most hammer prices for similar conditions (75) have been in the range of 170 to 280 euros.

3. Starting Price: The current starting price is 250 euros, suggesting that the seller has expectations for a hammer price in that range.

4. Market Trends: Given that the coin has been auctioned 29 times and has had a good sales percentage (26 out of 29), this indicates a consistent interest in the coin.

Based on these factors, an estimated maximum purchase price could be in the range of 280 to 320 euros, considering that the average hammer price is 242 euros and there is potential for the price to rise due to demand and the coin's condition. However, it is important to keep in mind that the final price will depend on the competition in the auction and the willingness of other bidders.