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+), indicating that it is in relatively good shape. This suggests that its value should be in the upper range of previous auction prices for coins with a similar condition.

2. Previous Auction Prices: By looking at previous auction prices for coins with similar conditions (80-85), we can see that auction prices have varied, but there are examples of auctions reaching up to 266 euros (in December 2020) and others hovering around 150-220 euros in recent auctions.

3. Average Auction Price: The average auction price for this coin is 153.77 euros, which provides a good reference for the expected value.

4. Starting Price: The current starting price is 140 euros, which is reasonable and aligns with previous auction prices.

5. Recent Trends: In the most recent auctions, the auction prices have shown a trend of being in the range of 180-240 euros for similar conditions.

Based on these factors, an estimated maximum purchase price could be in the range of 220 to 250 euros, considering that collector interest and demand may influence the final price. Therefore, a reasonable maximum purchase price could be 250 euros.