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

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

2. Auction History:
- In the past, this coin has been auctioned 4 times, of which it has sold 3 times. This indicates moderate interest in the coin.
- Previous hammer prices are quite varied, with a maximum price of 540 euros in a 2012 auction, but there is also a hammer price of 95 euros in 2024, suggesting that the value can fluctuate significantly depending on the condition and market interest at that time.

3. Starting Price and Average Prices:
- The current starting price is 30 euros, which is quite low compared to the average starting price of 180 euros and the average hammer price of 317.5 euros. This could indicate that the coin is not receiving the expected interest in this auction.

4. Comparison with Previous Prices:
- The condition of 30 (BC+) is lower than the conditions of 70 and 75 from previous auctions, suggesting that the hammer price could be lower this time.

Taking all these factors into account, an estimated maximum purchase price could be in the range of 50 to 80 euros. This is based on the current condition and moderate interest in the coin, as well as previous hammer prices. However, since the starting price is 30 euros, it may be possible to acquire it for a lower price if there is not much competition in the auction.