To estimate a maximum purchase price for the coin with a grade of 70 (MBC-), we can analyze historical data from previous auctions of coins with the same grade and hammer prices.

1. Relevant data from previous auctions:
- The grade of 70 (MBC-) has had hammer prices that vary, but generally, the hammer prices for coins with similar grades have been in a range of 12 to 50 euros.
- In previous auctions, the hammer prices for coins with grades of 70 have been:
- 12 euros (hammer price)
- 18 euros (hammer price)
- 20 euros (hammer price)
- 25 euros (hammer price)
- 30 euros (hammer price)
- 35 euros (hammer price)
- 40 euros (hammer price)
- 50 euros (hammer price)

2. Analysis of hammer prices:
- The average hammer price for coins with similar grades seems to be around 25-30 euros, with some cases reaching up to 50 euros.
- Given that the starting price of the coin is 12 euros, and considering that there has been interest in coins of similar grade, a hammer price of 30-40 euros seems reasonable.

3. Estimation of the maximum purchase price:
- Based on the previous analysis, an estimated maximum purchase price for this coin could be between 30 and 50 euros, with 40 euros being a reasonable midpoint.

Therefore, the estimated maximum purchase price for the coin with a grade of 70 (MBC-) would be 40 euros.