To estimate a maximum purchase price for the coin in question, we can analyze the provided data, including the current condition, previous starting and hammer prices, as well as trends in past auctions.

1. Current Condition: The coin has a condition of 70 (VF-). This is an important factor, as coins in better condition tend to achieve higher prices.

2. Starting and Hammer Prices:
- The current starting price is 400 euros.
- The average hammer price in previous auctions is 1056.92 euros, indicating that, in general, coins of this reference tend to sell for significantly higher prices than their starting price.

3. Analysis of Previous Prices:
- In past auctions, hammer prices have varied considerably, ranging from 360 euros to 4200 euros, depending on the condition of the coin.
- The condition of coins auctioned in the past has influenced the hammer prices. For example, a coin with a condition of 95 sold for 4200 euros, while others with a condition of 80 sold for lower prices (around 360-700 euros).

4. Trends:
- The general trend shows that coins with higher conditions (80 and above) tend to reach hammer prices that are at least 1.5 to 2 times their starting price.
- Given that the condition of the coin in question is 70, it is reasonable to expect that its hammer price will be below the hammer prices of coins with higher conditions.

5. Estimation of Maximum Purchase Price:
- Based on the average hammer price (1056.92 euros) and considering that the condition of this coin is lower than that of many sold in the past, an estimated hammer price could be in the range of 600 to 800 euros.
- Since the starting price is 400 euros, a reasonable maximum purchase price could be around 700 euros, taking into account the condition and previous hammer prices.

Conclusion: An estimated maximum purchase price for this coin could be approximately 700 euros.