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

1. Current Condition: The coin has a condition of 70 (MBC-). This is an important factor, as coins in better condition tend to reach higher prices.

2. Previous Auction Prices: By observing previous auction prices, we can see that coins with similar conditions have had varying hammer prices. For example:
- In previous auctions, coins with conditions of 70 have reached hammer prices of up to 140 euros (in the case of a coin with a condition of 95, but this can give an idea of the range).
- Most coins with conditions between 80 and 90 have had hammer prices ranging from 60 to 95 euros.

3. Average Hammer Price: The average hammer price for this coin is 64.35 euros, which can serve as a reference point.

4. Starting Price and Average Starting Price: The current starting price is 20 euros, and the average starting price is 39.16 euros. This suggests that there is considerable room for the hammer price to be higher.

5. Auction Trends: Given that the coin has been auctioned 33 times and has had a good sales percentage (28 out of 33), this indicates a consistent interest in the coin.

Based on these factors, an estimated maximum purchase price could be in the range of 70 to 90 euros, considering that the condition is 70 and there is interest in the coin. However, given the history of hammer prices, a reasonable maximum purchase price could be 80 euros. This allows for competition in the auction and aligns with previous hammer prices for coins of similar condition.