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 rating of 75 (MBC), indicating that it is in fairly good shape. This can positively influence its value.

2. Auction History:
- The average hammer price in previous auctions is 45.36 euros.
- The last auction with a similar condition (75) had a hammer price of 26 euros.
- In previous auctions, hammer prices have varied, but there are examples of sales reaching up to 160 euros for coins in better condition (90).

3. Starting Price and Average Starting Price:
- The current starting price is 20 euros, which is slightly higher than the average starting price of 19.59 euros. This suggests that the seller has expectations of a higher price.

4. Price Trends:
- Observing previous auctions, it seems that hammer prices have been increasing in some cases, especially for coins in better condition.

Based on these factors, an estimated maximum purchase price could be in the range of 50 to 70 euros. This is based on the fact that, although the condition is not the highest, the price history and the trend of increasing value for similar coins suggest that it could reach a higher price at auction.

Therefore, a reasonable estimated maximum purchase price could be 65 euros.