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 relatively good shape.

2. Previous auction prices:
- In 2018, the coin was auctioned with a starting price of 90 euros and sold for 240 euros, with a condition of 90.
- In 2022, it was auctioned with a starting price of 60 euros and sold for 380 euros, with a condition of 80.
- In 2015, there was an auction with a starting price of 300 euros and a final price of 360 euros, although the condition was not specified.

3. Average final price: The average final price for this coin is 229.6 euros, indicating that, in general, buyers are willing to pay significantly more than the starting price.

4. Current starting price: The starting price is 70 euros, which is relatively low compared to previous final prices.

5. Sales trends: The coin has been auctioned 7 times, of which it has sold 6 times, indicating good demand.

Given that the condition of the coin is 75 (MBC) and considering the previous final prices, an estimated maximum purchase price could be in the range of 250 to 300 euros. This is based on the fact that coins in similar conditions have reached final prices of up to 380 euros in the past, and the average final price is 229.6 euros.

Therefore, an estimated maximum purchase price could be approximately 280 euros.