To estimate a maximum purchase price for the coin in question, we can analyze the provided data:

1. Current starting price: 200 euros.
2. Auction history: The coin has been auctioned 12 times, of which it has sold 11 times. This indicates good demand.
3. Average hammer price: 185.36 euros, suggesting that, on average, coins of this reference sell for a price close to this value.
4. Previous prices:
- The highest hammer price was 650 euros in 2015, indicating that under exceptional conditions, the coin can reach significantly higher prices.
- The lowest hammer price was 12 euros, showing that there have also been sales under less favorable conditions.

5. Condition: There is no specific information about the condition of this coin, which may complicate the estimation. However, the history shows that there have been coins in different states of preservation.

Given that the starting price is 200 euros and considering the average hammer price of 185.36 euros, an estimated maximum purchase price could be situated between the starting price and the highest hammer price in the past.

Estimation: A reasonable maximum purchase price could be approximately 300 euros. This is based on the fact that the starting price is 200 euros and that, in the past, higher prices have been reached, but it should also be considered that the average hammer price is lower than the current starting price.