To estimate a maximum purchase price for the coin in question, we will consider several factors:

1. Current Condition: The coin has a condition rating of 75 (MBC), indicating that it is in quite good shape. This suggests that its value could be in the upper range of previous auctions.

2. Auction History:
- The average hammer price for similar coins has been 76 euros.
- In previous auctions, hammer prices for coins with a similar condition (75) have varied, but there are examples of sales reaching up to 130 euros (such as in the auction on February 16, 2023).

3. Starting Price: The current starting price is 30 euros, which is relatively low compared to previous hammer prices.

4. Sales Trends: The coin has been sold in 18 out of 21 auctions, indicating good demand and consistent interest in this reference.

Based on these factors, an estimated maximum purchase price could be in the range of 80 to 130 euros, considering that the average hammer price is 76 euros and there are precedents for higher hammer prices for coins in similar conditions.

Therefore, a reasonable estimated maximum purchase price could be 100 euros. This is based on the trend of hammer prices and the current condition of the coin.