To estimate a maximum purchase price for the coin in question, we can analyze the provided data and consider several factors:

1. Current Condition: The coin has a condition of 75 (MBC), which indicates that it is in fairly good shape, but not the best possible condition. This may influence the price, as coins in better condition tend to fetch higher prices.

2. Auction History:
- It has been auctioned 4 times in the past, of which 3 have sold. This indicates an interest in the coin.
- Previous hammer prices are relevant. For example, in a 2022 auction, a coin with a condition of 70 sold for 1000 euros, and another with a condition of 80 sold for 1600 euros. This suggests that the price can vary significantly depending on the condition.

3. Starting Price and Average Hammer Price:
- The current starting price is 1000 euros, and the average hammer price in the past has been 1433.33 euros. This suggests that the hammer price could be in a similar or higher range than the starting price.

4. Price Trends: Given that the average hammer price has been above the starting price, and considering that the condition of the coin is relatively good (75), it is reasonable to assume that the hammer price could be in a high range.

Based on these factors, an estimated maximum purchase price could be between 1200 and 1600 euros, considering that the condition is slightly lower than that of coins that have sold for higher prices. A price of 1400 euros could be a good benchmark for a competitive offer, given the price history and current condition.