To estimate a maximum purchase price for the coin in question, let's consider several factors:

1. Starting Price: 300 euros.
2. Condition: The coin has a condition rating of 70 (VF-), indicating that it is in quite good shape.
3. Auction History:
- In December 2021, the coin was auctioned with an estimated price of 200 euros and sold for 500 euros, indicating high demand and good interest in the coin at that condition.
- In February 2023, the starting price was 150 euros, with an estimated price of 300 euros, but it sold for 190 euros, suggesting that interest was lower on that occasion.

4. Average Hammer Price: 345 euros, which is a good indicator of market value.

Given that the coin has a starting price of 300 euros and considering the auction history, the average hammer price, and the condition, an estimated maximum purchase price could be around 500 euros, which is the highest price reached in the previous auction. However, since interest may vary, a more conservative range could be between 400 and 450 euros.

Therefore, a reasonable estimated maximum purchase price could be 450 euros.