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+), which indicates that it is not in very good shape. This generally reduces its value compared to coins in better condition.

2. Auction History:
- The average hammer price for similar coins in the past has been 94.91 euros.
- The coin has been auctioned 96 times, of which it has sold 81 times, indicating good demand.
- Previous hammer prices for coins with similar conditions (30) have varied, but the most recent price of 20 euros (in 2023) may be a good indicator.

3. Starting Price and Average Starting Price:
- The current starting price is 12 euros, which is quite low compared to the average starting price of 77.73 euros for similar coins.

4. Recent Trends:
- In recent auctions, hammer prices for coins with similar conditions have been in the range of 20 to 30 euros.

Based on these factors, an estimated maximum purchase price for this coin could be between 25 and 35 euros, considering that the condition is not optimal and the starting price is relatively low. This also takes into account the price trend in recent auctions and the sales history.

Therefore, a reasonable maximum purchase price could be 30 euros.