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 75 (MBC), indicating that it is in quite good shape. This generally translates to a higher price compared to coins with lower conditions.

2. Auction History:
- The average hammer price for similar coins is 136.12 euros.
- In the past, coins with similar conditions (around 70-80) have reached hammer prices of up to 140 euros (as seen in the April 2021 auction).

3. Starting Price and Previous Prices:
- The current starting price is 30 euros, which is relatively low compared to the average hammer price.
- In previous auctions, hammer prices have varied, but there are examples of coins with similar conditions that have reached hammer prices ranging from 75 to 850 euros, depending on the condition and demand.

4. Sales Trends: The coin has sold in 18 out of the last 22 auctions, indicating a consistent interest in this reference.

Based on these factors, an estimated maximum purchase price for this coin could be in the range of 120 to 150 euros, considering its good condition and the history of hammer prices in previous auctions. This allows for some margin for competition in the auction and the possibility that other bidders may also be interested.