To estimate a maximum purchase price for the coin with a grade of 70 (MBC-), we can analyze historical data from previous auctions and consider several factors:

1. Grade: A grade of 70 (MBC-) is an intermediate level. In the past, coins with a similar grade have had auction prices that vary considerably, but they generally fall within a range of 60 to 135 euros.

2. Previous auction prices: By observing the auction prices of coins with a grade of 70, we find:
- 2020-09-17: 95 euros
- 2018-12-11: (not available, but estimated at 130)
- 2018-09-19: 135 euros
- 2022-04-26: 110 euros
- 2023-05-23: (not available, but estimated at 90)

3. Price trends: The average auction price for this coin is 143.21 euros, indicating that there is potential for an increase in the auction price in future sales.

4. Average starting price: The average starting price is 81.39 euros, suggesting that buyers are willing to pay more than the starting price on many occasions.

5. Competition analysis: Given that there is an auction scheduled in the coming days, competition may influence the final price. If there is significant interest, the price could increase.

Based on these factors, an estimated maximum purchase price for the coin with a grade of 70 (MBC-) could be in the range of 120 to 150 euros. This takes into account both the historical auction prices and the general trend of increasing interest in coins of this grade.