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.

2. Auction History:
- The average hammer price for similar coins in the past is 73.76 euros.
- The coin has been auctioned 111 times, of which it has sold 102 times, indicating good demand.
- Previous hammer prices for coins with similar conditions (around 75) have varied, but there are examples of auctions reaching up to 220 euros for higher conditions.

3. Starting Price and Previous Prices:
- The current starting price is 20 euros, which is relatively low compared to the average hammer price.
- In previous auctions, coins with similar conditions have had hammer prices ranging from 30 to 100 euros, depending on demand and condition.

4. Recent Trends:
- In the most recent auctions, hammer prices have shown an increase, suggesting that demand may be growing.

Based on these factors, an estimated maximum purchase price for this coin could be between 80 and 120 euros. This is based on the average hammer price and the condition rating, as well as the price trend in recent auctions.

Therefore, a reasonable maximum purchase price could be 100 euros.