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 quite good shape. This generally translates to a higher price compared to coins with lower conditions.

2. Auction History:
- The average hammer price for coins with a similar condition (75) has been between 70-80 euros in previous auctions.
- Specifically, in the 2020 auctions, the hammer price was 80 euros, suggesting that there is significant interest in coins of this condition.

3. Starting Price and Average Starting Price:
- The current starting price is 45 euros, which is below the average starting price of 54.76 euros. This could indicate a good buying opportunity.

4. Sales Trends: The coin has sold in 20 out of the 22 previous auctions, indicating good demand and a history of successful sales.

5. Previous Estimates: In past auctions, the estimated price for coins of similar condition has ranged from 50 to 150 euros, depending on the condition and other factors.

Taking all these factors into account, an estimated maximum purchase price for this coin could be around 80-90 euros. This is based on the historical hammer prices for coins of similar condition and the demonstrated interest in previous auctions.