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 75 (MBC), indicating that it is in fairly good shape, but not the best possible condition.

2. Auction History:
- The average hammer price for coins of similar condition (75) has been approximately 220-300 euros in previous auctions.
- In the most recent auctions, the hammer price has varied, but it has reached up to 950 euros in an auction with a condition of 95, indicating that the value can increase significantly with better condition.

3. Starting Price and Average Hammer Price:
- The current starting price is 150 euros, and the average hammer price in the past has been 300.94 euros, suggesting there is potential for an increase in the hammer price.

4. Sales Trends: The coin has been sold in 19 out of 20 auctions, indicating good demand.

5. Comparison with Previous Prices:
- In previous auctions with a condition of 75, hammer prices have ranged from 175 to 300 euros.

Based on these factors, an estimated maximum purchase price for the coin could be in the range of 300 to 350 euros. This is based on the historical hammer price data and the current condition of the coin. However, it is important to note that the final price may vary depending on the competition in the auction and the interest from other buyers.