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

1. Starting price: 70 euros.
2. Current condition: 75 (MBC), indicating good condition.
3. Auction history:
- In 2020, a coin in condition 95 was auctioned with a starting price of 600 euros and a final price of 850 euros.
- In 2022, a coin in condition 70 had a starting price of 15 euros and a final price of 160 euros.

4. Average starting and final prices: The average starting price is 228.33 euros and the average final price is 363.33 euros.

Given that the current condition of the coin is 75, which is better than the 70 condition in the 2022 auction but lower than the 95 condition in the 2020 auction, we can make an estimation.

- The difference in condition between 75 and 95 is significant, suggesting that the final price will not reach 850 euros, but it could be closer to the 160 euro range from the 2022 auction, adjusted for the better condition.

- Considering the average final price of 363.33 euros and the price history, an estimated maximum purchase price could be positioned between the average final price and the final price of the 2022 auction.

Taking all these factors into account, an estimated maximum purchase price for the coin could be around 300 to 400 euros. This reflects good condition and price history, but also considers that it will not reach the highest levels due to the difference in condition.