To estimate a maximum purchase price for the coin in question, we will consider several factors:

1. Condition: The coin has a condition of 70 (VF-), which indicates that it is in fairly good shape, but not the best possible condition. This can influence the price, as coins in better condition tend to fetch higher prices.

2. Auction History:
- In the past, this coin has been auctioned 4 times, of which it has sold 3 times. This indicates a consistent interest in the coin.
- Previous hammer prices have been 320 (2020), 261 (2020), and 320 (2022). The highest hammer price was 320, which sets an upper limit on the value that buyers are willing to pay.

3. Starting Price and Estimates:
- The current starting price is 300 euros, which is slightly lower than the previous average hammer price (300.33 euros).
- The average starting price in previous auctions was 280 euros, suggesting that the current starting price is reasonable.

4. Price Trends:
- The last auction scheduled for September 2024 has a starting price of 350 euros and an estimated price of 450 euros, suggesting that interest and value in the coin may be increasing.

Taking all these factors into account, an estimated maximum purchase price could be around 320-350 euros. This is based on the previous highest hammer price and the growing interest in the coin. However, since the current starting price is 300 euros, it may be wise not to exceed 350 euros to ensure a competitive purchase.

Maximum purchase estimate: 350 euros.