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 is relatively low compared to other coins that have been auctioned in the past. This can significantly affect its value.

2. Previous Auction Prices: By observing the auction prices of similar coins in higher condition (for example, 75 or 90), prices have varied considerably, reaching figures of up to 4000 euros in some cases. However, for coins in lower conditions, the auction prices are much lower.

3. Average Auction Price: The average auction price for this coin is 406.31 euros, indicating that, in general, coins of this reference tend to sell at relatively high prices, but this is based on more favorable condition.

4. Starting Price: The starting price is 50 euros, suggesting that the auction house expects moderate interest in the coin.

5. Recent Trends: Recent auctions have shown increasing interest in coins, but they have also reflected variability in prices depending on condition.

Given that the condition of this coin is 30 (BC+), and considering previous auction prices and the average price, an estimated maximum purchase price could be in the range of 150 to 250 euros. This is based on the idea that, although the coin has a potential higher value in better condition, its current state will limit its appeal and, therefore, its auction price.

Maximum Purchase Estimate: 250 euros.