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

1. Condition: The coin has a condition of 70 (MBC-), which indicates that it is in quite good shape. This generally translates to a higher value compared to coins with lower conditions.

2. Auction History:
- In the past, the coin has been auctioned 5 times, of which it has sold 3 times. This suggests that there is moderate interest in the coin.
- Previous hammer prices for coins with the same condition (70) have reached up to 65 euros, and the average hammer price is 50 euros.

3. Starting Price and Estimates:
- The current starting price is 25 euros, which is reasonable given the history of starting and hammer prices.
- The average hammer price of 50 euros suggests that there is potential for the coin to sell at a higher price.

4. Recent Trends:
- In the most recent auction, a coin with a condition of 30 sold for 35 euros, indicating that interest may be increasing.

Based on these factors, an estimated maximum purchase price could be in the range of 60 to 70 euros, as this is the price range seen in previous auctions for coins in similar conditions. However, since the starting price is 25 euros, it is likely that the hammer price will not significantly exceed the average hammer price of 50 euros, unless there is exceptional interest in the coin.

Therefore, a reasonable estimated maximum purchase price could be 65 euros.