To estimate a maximum purchase price for the coin in question, we can analyze the provided data:

1. Current condition: The coin has a condition of 75 (MBC), indicating that it is in quite good shape.

2. Previous auction prices:
- In 2019, the coin was auctioned with a starting price of 60 euros and sold for 64 euros, suggesting that interest in the coin was high at that time.
- In 2014, it was also auctioned with a starting price of 60 euros and sold for 60 euros, indicating that the final price was equal to the starting price, but it did not sell for a higher price.
- The starting and final prices in previous auctions varied, but the highest final price was 64 euros.

3. Average final price: The average final price of 51.75 euros suggests that, in general, coins of this reference tend to sell below their starting price.

4. Sales trends: Out of the 6 previous auctions, 4 resulted in sales, indicating moderate interest in the coin.

Given that the condition is good (75), and considering the previous final prices, an estimated maximum purchase price could be slightly above the previous highest final price (64 euros), while also taking into account the average final price.

Therefore, a reasonable estimated maximum purchase price could be 70 euros. This reflects interest in the coin, but is also conservative in relation to previous final prices.