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

2. Historical Prices: By looking at the auction prices of coins with similar conditions, we can see that:
- In December 2019, a coin with a condition of 30 was auctioned for 35 euros.
- In July 2020, another coin with a condition of 75 was auctioned for 64 euros.
- In April 2022, a coin with a condition of 30 was auctioned for 70 euros.

3. Average Auction Price: The average auction price for this coin in the past has been 104.5 euros, but this includes coins in better conditions.

4. Starting Price and Estimates: The current starting price is 30 euros, and the average starting price in the past has been 82.86 euros.

5. Recent Trends: In the most recent auctions, the auction prices for coins with similar conditions have varied, but have not exceeded 70 euros.

Based on these factors, an estimated maximum purchase price for this coin, considering its condition and historical prices, could be between 50 and 70 euros. Given that the condition is not high, a more conservative price would be approximately 60 euros as a maximum.