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

1. Coin Condition: The coin has a condition rating of 75 (MBC), indicating average quality. This can influence the price, as coins in better condition tend to fetch higher prices.

2. Starting Price and Previous Prices: The current starting price is 70 euros. In previous auctions, the average hammer price for coins of similar condition has varied, with some prices reaching up to 732.53 euros for coins in better condition (90) and others in similar conditions (75) selling for prices ranging between 95 and 180 euros.

3. Price Trends: The average hammer price for coins in condition 75 has been approximately 231.8 euros. This suggests that, although the starting price is low, the potential selling price could be considerably higher.

4. Historical Data: By looking at the hammer prices of similar coins in the past, it can be seen that there is significant variability. However, the highest recorded price for a coin in condition 75 was 800 euros, indicating that there is a market willing to pay high prices for quality coins.

Based on these factors, an estimated maximum purchase price for this coin could be in the range of 200 to 300 euros. This is based on the average hammer price and the price trend for coins of similar condition. However, it is important to note that the final price may vary depending on demand at the auction and other market factors.