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

1. Current Condition: The coin has a condition rating of 80 (MBC+), indicating that it is in quite good shape. This suggests that its value should be above that of coins with lower conditions.

2. Auction History:
- The average hammer price for coins of this reference is 757.22 euros.
- In previous auctions, hammer prices have varied, but there are examples of coins with similar conditions that have sold for prices ranging from 340 to 380 euros.
- The most recent auction with a condition of 100 reached a hammer price of 3000 euros, indicating a strong market for high-condition coins.

3. Starting Price and Average Starting Price:
- The current starting price is 250 euros, which is below the average starting price of 330 euros. This could indicate a buying opportunity at a reasonable price.

4. Sales Trends: The coin has been sold in 9 out of the last 10 auctions, suggesting there is consistent interest in this coin.

Based on these factors, an estimated maximum purchase price could be in the range of 600 to 800 euros, considering that the condition is good and the auction price history supports a higher value. However, since the starting price is 250 euros, it could be a good opportunity to acquire it at a lower price if competition in the auction remains.

Therefore, a reasonable maximum purchase price could be 750 euros.