To estimate a maximum purchase price for the coin in question, we can analyze 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 hammer price for similar coins in the past is 146.6 euros.
- The coin has been auctioned 15 times, of which it has sold 11 times, indicating good demand.
- Previous hammer prices for this coin varied, but there are examples of auctions reaching up to 650 euros in superior conditions.

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 62.92 euros.

4. Recent Trends: In the most recent auction, the coin was offered at a starting price of 12 euros and was estimated at 20 euros, although it did not sell. This may indicate that interest in this coin has decreased or that the starting price is not attractive.

5. Condition of Similar Coins: Coins with higher conditions (such as 70, 75, 80, 85) have reached significantly higher hammer prices. This suggests that condition is a critical factor in determining price.

### Estimated Maximum Purchase Price
Given that the condition of the coin is 30 (BC+), and considering the auction price history and the average starting price, a reasonable maximum purchase price could be:

- Estimated Maximum Price: 30-40 euros.

This range takes into account the current condition and historical interest in the coin, as well as the fact that the starting price is low. If the auction generates interest, the price could approach the upper end of this range.