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

1. Coin Condition: The coin has a condition rating of 80 (MBC+), indicating that it is in quite good shape. This generally translates to a higher price compared to coins with lower conditions.

2. Previous Prices: By observing the auction prices of coins with a similar condition (80), we can see that they have reached auction prices that vary, but some examples are:
- 2020-09-17: Auction price 31 (condition 80)
- 2019-07-03: Auction price 63 (condition 85)
- 2018-10-16: Auction price 65 (condition 80)

3. Average Auction Price: The average auction price for this coin is 128.83 euros, suggesting that, in general, coins of this reference tend to sell for relatively high prices.

4. Starting Price: The starting price is 40 euros, which is quite low compared to the average auction price.

5. Auction Trends: The coin has been auctioned 266 times, with an 84% sell-through rate (224 times sold). This indicates good demand and liquidity in the market.

Based on these factors, an estimated maximum purchase price could be set in a range that considers the average auction price and the coin's condition. Given that the average auction price is 128.83 euros and considering that the condition is 80, a reasonable maximum purchase price could be:

Estimated maximum purchase price: 150 euros.

This price reflects a balance between the condition, historical demand, and the average auction price, allowing for a margin for competition in the auction.