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

1. Starting price: 200 euros.
2. Current grade: 70 (VG-), which is an average grade.
3. Auction history:
- In the auction on April 28, 2022, a coin with a grade of 80 sold for 386 euros.
- In the auction on March 14, 2024, a coin with a grade of 70 sold for 182 euros.
- In the auction on May 27, 2024, another coin with a grade of 80 sold for 700 euros.

4. Average prices:
- Average starting price: 227.5 euros.
- Average hammer price: 422.67 euros.

Given that the grade of the coin to be auctioned is 70 (VG-), and considering that in the past a coin with the same grade sold for 182 euros, this suggests that the hammer price may be in a similar range.

However, we must also consider the starting price of 200 euros and the fact that the average hammer price is significantly higher (422.67 euros). This indicates that there is potential for the coin to sell for a higher price, especially if there is interest in the auction.

Taking all these factors into account, an estimated maximum purchase price could be positioned between the average hammer price and the hammer price of the previous auction with a similar grade.

Therefore, an estimated maximum purchase price could be around 300-350 euros. This reflects a balance between the grade, the price history, and the potential interest in the auction.