To estimate a maximum purchase price for the coin in question, we can 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 generally reduces its value compared to coins in better condition.

2. Auction History:
- The average starting price for similar coins is 183.72 euros, and the average hammer price is 229.86 euros.
- In the past, coins of this reference have been auctioned with hammer prices that varied significantly, from low prices (like 20 euros) to much higher prices (like 1153.23 euros in much better condition).

3. Sales Trends: The coin has sold in 30 out of 39 auctions, indicating good demand. However, the fact that there have been 9 auctions where it did not sell suggests that the starting price may be a determining factor.

4. Current Starting Price: The starting price is 30 euros, which is relatively low compared to the average starting price of other similar coins.

Given that the condition of the coin is low and the starting price is 30 euros, an estimated maximum purchase price could be in a range that considers the condition and the price history.

Taking all these factors into account, an estimated maximum purchase price could be around 70-90 euros. This is based on the fact that, although the condition is not high, the interest in the coin and the price history suggest that it could reach a higher price than the starting price, but not so much as to exceed the hammer prices of coins in better condition.