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 quite good shape. This generally translates to a higher price compared to coins in lower condition.

2. Auction History:
- The average hammer price for similar coins is 237.17 euros, suggesting that there is a market willing to pay significantly higher prices than the starting price.
- In previous auctions, hammer prices have varied, but there are examples of sales reaching up to 1200 euros for coins in similar conditions.

3. Starting Price and Average Starting Price:
- The current starting price is 50 euros, which is quite low compared to the average hammer price. This could indicate a good buying opportunity.

4. Sales Trends: The coin has been sold in 12 out of the 13 times it has been auctioned, indicating good demand.

5. Comparison with Previous Prices:
- In previous auctions, coins with similar conditions have reached hammer prices ranging from 45 to 1100 euros, showing a wide price range depending on demand and condition.

Based on these factors, an estimated maximum purchase price could be in the range of 200 to 300 euros, considering that the average hammer price is 237.17 euros and that the coin's condition is good. However, given the history of higher hammer prices, it might be reasonable to consider a maximum of up to 400 euros if demand is strong in the auction.