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 80 (MBC+), indicating that it is in relatively good shape. This suggests that its value should be above that of coins with lower conditions.

2. Auction History:
- The average hammer price in previous auctions is 256.8 euros, indicating that, in general, coins of this reference tend to sell for significantly higher prices than their starting price.
- The highest recorded auction price was 1100 euros for a coin with a condition of 100, which sets a high ceiling, but it is also important to consider that the condition of that coin is superior.

3. Starting Price and Average Starting Price:
- The current starting price is 30 euros, which is quite low compared to the average hammer price. This suggests that there is significant potential for the final price to be much higher.

4. Sales Trends: Of the 15 times it has been auctioned, it has sold 10 times, indicating good demand for this coin.

5. Condition-Based Estimation: Given that the condition of this coin is 80, we can estimate that its final price could be in an intermediate range between the lowest and highest auction prices.

Taking all these factors into account, an estimated maximum purchase price could be in the range of 200 to 300 euros. This is based on the auction price history and the current condition of the coin. However, it is important to remember that the final price may vary depending on competition in the auction and the interest of collectors.