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 fairly good shape, but not the best possible condition.

2. Auction History:
- The average hammer price for similar coins has been 87.81 euros.
- In previous auctions, hammer prices for coins with a similar condition (75) have varied, but there are examples where hammer prices have reached up to 90 euros.

3. Starting Price: The starting price is 50 euros, which may influence the perception of the coin's value.

4. Sales Trends: Out of the 18 times it has been auctioned, 16 have been sold, indicating good demand.

5. Previous Prices: In past auctions, the hammer price has ranged from 45 to 460 euros, but the most relevant prices are those close to the current condition.

Based on these factors, an estimated maximum purchase price could be around 90 euros, as this is a price that has been reached in previous auctions for coins with a similar condition and aligns with the average hammer price. However, it is important to consider that collector interest and competition in the auction can also influence the final price.