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

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. Previous Prices: By looking at previous auction prices for coins with a similar condition (80), we can see that they have reached hammer prices of up to 150 euros in recent auctions. For example, at the auction on December 16, 2020, the coin with a condition of 80 was sold for 150 euros.

3. Starting Price and Average Hammer Price: The current starting price is 140 euros, and the average hammer price for this coin in the past has been 132.77 euros. This suggests that the starting price is reasonable and could attract bidders.

4. Auction Trends: The coin has been auctioned 81 times, with a sell-through rate of 97.5% (79 out of 81). This indicates a consistent interest in this coin, which may influence the hammer price.

5. Comparison with Estimated Prices: In previous auctions, estimated prices for coins with similar conditions have varied, but some have reached up to 200 euros in the case of coins with higher conditions (95).

Based on these factors, an estimated maximum purchase price for the coin in question could be between 150 and 180 euros, considering that the interest in the coin and its condition are favorable. Therefore, a reasonable maximum purchase price could be 170 euros.