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

1. Current Condition: The coin has a condition of 70 (VF-), which is lower than the conditions of previously auctioned coins (80 and 85). This suggests that its value may be less than that of coins in better condition.

2. Previous Prices:
- In the December 2020 auction, the coin with a condition of 80 sold for 320 euros, and in November 2020, the coin with a condition of 85 sold for 360 euros.
- The average hammer price for previous auctions is 360 euros, indicating that, in general, coins of this reference tend to sell close to this price.

3. Starting Price: The current starting price is 350 euros, which is slightly higher than the average hammer price of previous auctions. This may indicate that the seller has high expectations, but it could also reflect current demand.

4. Sales Trends: Since the coin has been sold every time it has been auctioned, this suggests there is consistent interest in this reference.

Taking all these factors into account, an estimated maximum purchase price could be in the range of 300 to 340 euros, considering that the condition is lower than the coins sold previously and that the starting price is 350 euros. A price of 340 euros could be a good starting point for an offer, as it is below the starting price and reflects the condition of the coin.