To estimate a maximum purchase price for the coin in question, we can analyze the provided data, especially the current grade of the coin (70, MBC-) and previous auction prices.

1. Grade: The coin has a grade of 70 (MBC-), indicating that it is in an acceptable condition, but not of high quality. This suggests that its price will not reach the highest auction levels.

2. Previous auction prices:
- In previous auctions, we have seen hammer prices that vary significantly depending on the grade. For example:
- A hammer price of 25 euros with a grade of 75.
- A hammer price of 160 euros with a grade of 85.
- A hammer price of 51 euros with a grade of 70.

3. Price trends:
- The average hammer price for this coin is 129.25 euros, but this includes coins of different grades.
- The trend shows that as the grade improves, the hammer price also tends to increase.

4. Estimation:
- Given that the grade of the coin is 70, and considering that in previous auctions with a similar grade, hammer prices have reached up to 51 euros, we can estimate that the maximum purchase price could be in a similar range or slightly higher, as the market may have changed.

Based on this analysis, an estimated maximum purchase price for the coin in grade 70 could be approximately 60-70 euros. This takes into account the possibility that interest in the coin may have increased since the previous auctions.