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

1. Coin Condition: The coin to be auctioned 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 condition ratings.

2. Auction History:
- The average hammer price for similar coins has been 64.87 euros.
- In previous auctions, the hammer prices for coins with a similar condition (80) have varied, but the highest recorded price was 92 euros in a past auction.

3. Starting Price: The starting price is 50 euros, which is a good starting point, but given the history of hammer prices, it is likely that the final price will be significantly higher.

4. Sales Trends: Out of the 19 times this coin has been auctioned, it has sold 15 times, indicating good demand.

Based on these factors, an estimated maximum purchase price could be between 80 and 100 euros, considering that the highest hammer price in the past was 92 euros and that the coin's condition is good. Therefore, a reasonable maximum purchase price could be 90 euros.