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 an acceptable state, but not of the highest quality.

2. Auction History:
- The average hammer price for this coin in the past is 1421.05 euros.
- It has been auctioned 20 times, of which 14 have sold, indicating good demand.
- Previous hammer prices for coins with a similar condition (75) have varied, but there are examples of auctions reaching up to 625 euros (2012) and 350 euros (2011).

3. Price Trends:
- In previous auctions, hammer prices for coins with a condition of 75 have ranged between 180 and 625 euros.
- The most recent auction with a condition of 85 had an estimated price of 400 euros, suggesting that the value may increase with better condition.

4. Estimation: Given that the condition of the coin is 75, and considering the auction price history, a reasonable maximum purchase price could be in the range of 400 to 600 euros. This is based on the fact that the average hammer price is 1421.05 euros, but since the condition is not optimal, the price should be adjusted downward.

Estimated maximum purchase price: 600 euros.