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

1. Condition: The coin has a condition rating of 85 (ebc-), indicating that it is in quite good shape. This can positively influence its value.

2. Auction History:
- It has been auctioned 4 times in the past, of which it has sold 3 times. This suggests that there is interest in the coin.
- The average starting price in previous auctions is 172 euros, and the average hammer price is 158.67 euros. This indicates that, in general, the coin has sold for below its starting price.

3. Previous Prices:
- In the 2016 auction, the coin started at 250 euros and sold for 260 euros, showing that at that starting price, the coin has sales potential.
- In other auctions, the hammer prices have been lower, but they have also sold at lower starting prices.

4. Current Starting Price: The current starting price is 250 euros, which is consistent with previous starting prices.

Given that the coin has a history of successful sales at prices close to or above its current starting price, and considering its good condition, an estimated maximum purchase price could be around 300-350 euros. This is based on the estimated price from previous auctions and the demonstrated interest in past auctions.

Therefore, a reasonable maximum purchase price could be 350 euros.