To estimate a maximum purchase price for the coin in question, let's consider several factors:

1. Current condition: The coin has a condition rating of 30 (BC+), indicating that it is in a fairly deteriorated state. This will negatively affect its value compared to coins in better condition.

2. Auction history: The coin has been auctioned previously with an estimated price of 2000 euros and a hammer price of 1360 euros in a condition of 75. This suggests that the value could be significantly higher in better conditions.

3. Average hammer price: The average hammer price for this coin in the past has been 1080 euros, providing an additional reference point.

4. Starting price: The current starting price is 150 euros, indicating that the seller is looking for a low initial price, possibly to attract more bidders.

Given that the current condition is quite low (30), and considering the price history, a reasonable maximum purchase price could be in the range of 300 to 400 euros. This is based on the fact that, although the previous hammer price was 1360 euros, the current condition of the coin significantly limits its value.

Therefore, an estimated maximum purchase price could be 350 euros.