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

1. Current Condition: The coin has a condition of 75 (MBC), which indicates that it is in fairly good shape, but not the best possible condition.

2. Auction History:
- The average hammer price for similar coins in the past is 445.26 euros.
- The coin has been auctioned 24 times, of which it has sold 21 times, indicating good demand.
- Previous hammer prices for coins with similar conditions (75) have varied, but there are examples of auctions reaching up to 440 euros.

3. Starting Price and Average Starting Price:
- The current starting price is 280 euros, which is slightly higher than the average starting price of 243.75 euros.

4. Price Trends:
- In previous auctions, hammer prices for coins with conditions of 75 have ranged from 200 to 440 euros.

Based on this data, an estimated maximum purchase price could be in the range of 400 to 450 euros, considering that the coin is in good condition and that the price history shows it can reach higher values at auctions.

Therefore, an estimated maximum purchase price could be 450 euros.