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, but not among the best qualities.

2. Auction History:
- The average hammer price in previous auctions is 411.1 euros.
- The last auction for this coin had a hammer price of 800 euros, suggesting significant interest in coins of this reference, especially in good condition.
- Previous hammer prices for coins with similar conditions (80-85) have ranged between 226 and 600 euros.

3. Starting Price and Average Starting Price: The current starting price is 300 euros, and the average starting price in the past has been 280.77 euros.

4. Sales Trends: The coin has sold in 11 of the last 14 auctions, indicating good demand.

Based on this data, an estimated maximum purchase price could be in the range of 450 to 600 euros. This is based on the interest shown in previous auctions and the average hammer price. Given that the condition is 80, a more conservative price could be around 450 euros, while if there is strong competition in the auction, it could reach up to 600 euros.

Therefore, a reasonable estimated maximum purchase price would be 550 euros.