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

1. Current Condition: The coin has a condition of 75 (MBC), indicating that it is in an acceptable state, but not of the highest quality.

2. Auction History:
- The average hammer price for coins of similar condition (75) in the past has been approximately 40-45 euros.
- In previous auctions, coins with a condition of 75 have reached hammer prices of up to 40 euros.

3. Starting Price and Average Hammer Price:
- The current starting price is 20 euros, which is quite low compared to the average hammer price of 64.84 euros.
- The average starting price has been 39.18 euros, suggesting there is potential for an increase in the hammer price.

4. Price Trends:
- In recent auctions, hammer prices for coins of similar condition have ranged between 30 and 50 euros, with some exceptional cases reaching up to 95 euros for higher conditions.

Based on these factors, an estimated maximum purchase price for this coin could be between 40 and 50 euros, considering that the condition is 75 and that the price history shows that coins in similar conditions have reached those values.

Therefore, a reasonable maximum purchase price could be 45 euros.