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 good condition. This generally translates to a higher price compared to coins with lower conditions.

2. Previous Auction Prices: By observing previous auction prices for coins with similar conditions (80 and 70), we can see that the highest auction price for a coin with a condition of 80 was 90 euros in December 2020. For coins with a condition of 70, auction prices have varied, but the highest was 100 euros.

3. Average Auction Price: The average auction price for this coin is 110.33 euros, suggesting that, in general, coins of this reference tend to reach higher prices.

4. Starting Price and Estimates: The starting price is 60 euros, and the average starting price in previous auctions is 43.77 euros. This indicates that the current starting price is relatively high, which could influence the final auction price.

5. Auction Trends: Given that there have been 13 previous auctions and 12 of them resulted in sales, this suggests a steady demand for this coin.

Taking all these factors into account, an estimated maximum purchase price could be around 90-110 euros, considering that the highest auction price for a coin in similar condition was 90 euros and that the average auction price is 110.33 euros.

Therefore, a reasonable maximum purchase price could be 100 euros. This allows for some margin for competition in the auction, given that the starting price is 60 euros.