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

1. Current Condition: The coin has a condition rating of 30 (BC+), indicating that it is not in the best condition. This may negatively affect its value compared to coins in better condition.

2. Auction History:
- The coin has been auctioned 9 times, of which it has sold 6 times. This indicates moderate interest in the coin.
- Previous hammer prices have varied, but there are some hammer prices close to 30 euros, such as in the auctions of 2023 and 2017.

3. Starting Price and Average Hammer Price:
- The current starting price is 30 euros, and the average hammer price in the past has been approximately 26.17 euros. This suggests that the starting price is reasonable, but it may not sell for much more than that.

4. Price Trends:
- Estimated prices in previous auctions have been higher than the hammer prices, suggesting that buyers may be willing to pay more than what it ultimately sells for.

5. Comparison with Previous Prices:
- In previous auctions, the hammer price has reached up to 40 euros under similar conditions, although this is not common.

Taking all these factors into account, an estimated maximum purchase price could be around 35-40 euros. This is based on the historical interest in the coin and the fact that the starting price is reasonable, but it should also be considered that the condition is not the best. Therefore, a price of 35 euros could be a good starting point for an offer.