To estimate a maximum purchase price for the coin in question, we can analyze the provided data, especially previous auction prices and the current condition of the coin.

1. Current Condition: The coin has a condition of 30 (BC+), which indicates that it is not in very good shape. This may affect its value compared to coins in better condition.

2. Previous Auction Prices:
- In previous auctions, we have seen hammer prices that vary significantly. For example:
- In 2020, a coin with a condition of 30 was auctioned for 24 euros.
- In other auctions, coins with higher conditions (80) have sold for prices around 40-50 euros.
- The average hammer price for this coin is 24.07 euros.

3. Price Trends:
- The coin has been auctioned 31 times, of which it has sold 29 times, indicating good demand.
- The average starting price is 18.68 euros, suggesting that buyers are willing to pay more than the starting price in most cases.

4. Estimation:
- Given that the condition is 30, and considering it has previously sold for 24 euros, a hammer price around 25-30 euros could be reasonable, taking into account that the market may be willing to pay a bit more due to demand.

Conclusion: Based on the information and analysis, an estimated maximum purchase price for this coin could be 30 euros.