To estimate a maximum purchase price for the coin that is going to be auctioned, we can consider several factors based on the provided data:

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

2. Starting Price and Previous Prices: The current starting price is 80 euros. In previous auctions, coins with the same condition (80) have had hammer prices that varied, but some have reached up to 400 euros (as in the December 2019 auction).

3. Average Hammer Price: The average hammer price for similar coins is 104.53 euros, suggesting that, on average, coins of this condition sell for above the starting price.

4. Auction Trends: The coin has been auctioned 72 times, of which 60 have been sold. This indicates good demand and a history of successful sales.

5. Previous Estimated Prices: In previous auctions, the estimated price for coins with a condition of 80 has been significantly higher than the current starting price. For example, on several occasions, the estimated price has exceeded 200 euros.

Based on these factors, an estimated maximum purchase price could be in the range of 150 to 250 euros, considering that the hammer price may be higher depending on demand and competition in the auction.

Therefore, a reasonable maximum purchase price could be 200 euros.