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

1. Current Condition: The coin has a condition rating of 80 (MBC+). This is an important factor, as coins in better condition tend to reach higher prices.

2. Starting Price: The starting price is 450 euros. This is the baseline for the auction.

3. Sales History: The coin has been auctioned 69 times, of which it has sold 67 times. This indicates high demand and a good sales record.

4. Previous Prices: By looking at previous hammer prices for coins with similar conditions (80-85), we can see that hammer prices have varied, but many have been in the range of 300 to 750 euros, depending on the condition and demand at that time.

5. Average Hammer Price: The average hammer price for this coin is 403.39 euros, suggesting that, on average, coins of this reference sell for a reasonable price.

6. Recent Trends: In the most recent auctions, hammer prices have been in the range of 550 to 700 euros for similar conditions, indicating that interest in this coin may be increasing.

Based on these factors, an estimated maximum purchase price for the coin in question could be in the range of 600 to 750 euros. This is due to the good condition, sales history, and recent trends in hammer prices.

Therefore, a reasonable maximum purchase price could be 700 euros.