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

1. Current Condition: The coin has a condition rating of 75 (MBC), indicating that it is in quite good shape. This generally translates to a higher price compared to coins with lower conditions.

2. Auction History:
- The average hammer price for similar coins in the past is 50.63 euros.
- The coin has been auctioned 20 times, of which it has sold 19 times, indicating good demand.
- Previous hammer prices for coins with similar conditions (70-80) have varied, but there are examples of auctions reaching up to 100 euros for higher conditions.

3. Starting Price and Estimates:
- The current starting price is 20 euros, which is relatively low compared to the average hammer price.
- The average starting price in the past has been 33.16 euros, suggesting that the current starting price could be attractive to buyers.

4. Recent Trends: In the most recent auctions, hammer prices have ranged from 20 to 80 euros, depending on the condition.

Based on these factors, an estimated maximum purchase price for this coin, considering its condition and auction history, could be between 70 and 90 euros. This is based on the trend of hammer prices for coins of similar condition and the demand observed in previous auctions.

Therefore, an estimated maximum purchase price could be 80 euros.