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

1. Coin Condition: The coin has a condition rating of 70 (MBC-), which indicates that it is in an acceptable state, but not excellent. This generally reduces its value compared to coins in better condition.

2. Auction History: The coin has been auctioned 57 times, of which it has sold 50 times. This indicates good demand. The average hammer price for similar coins in the past is 1164.61 euros, providing a benchmark.

3. Previous Prices: Previous hammer prices for coins with similar conditions (around 70) have varied, but there are examples of hammer prices exceeding 1000 euros. However, there are also lower prices, suggesting that the price may fluctuate depending on demand at the time of the auction.

4. Starting Price: The starting price is 120 euros, which is relatively low compared to the average hammer price. This may indicate that there is an opportunity to purchase at a reasonable price.

5. Market Trends: Given that the average starting price for similar coins is 654.7 euros, and the average hammer price is 1164.61 euros, we can infer that there is a considerable margin between the starting price and the hammer price.

Taking all these factors into account, an estimated maximum purchase price could be in the range of 800 to 1000 euros. This is based on the hammer price history and the condition of the coin. However, it is important to pay attention to the demand in the specific auction, as this can influence the final price.