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 85 (ebc-), indicating that it is in fairly good shape, although not the best possible condition.

2. Auction History:
- In 2011, the coin was estimated at 130 euros and sold for 180 euros.
- In 2021, it was estimated at 300 euros but did not sell, which could indicate that the price was too high for the market at that time.

3. Average Hammer Price: The average hammer price for this coin has been 180 euros, providing a solid reference.

4. Auction Frequency: The coin has been auctioned 3 times in the past, of which it has only sold once. This may indicate limited interest in the coin, which could affect its price.

5. Starting Price: The starting price is 50 euros, which is relatively low compared to previous hammer prices.

Given that the current condition is good (85), and considering the average hammer price of 180 euros, as well as the auction history, an estimated maximum purchase price could be in the range of 180 to 250 euros. This is because, although the previous hammer price was 180 euros, the condition and market interest could justify a higher price.

Therefore, a reasonable estimated maximum purchase price could be 250 euros.