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

1. Coin Condition: The coin has a condition rating of 70 (MBC-), indicating that it is in relatively good shape, but not of the highest quality (FDC).

2. Auction History:
- The average hammer price for similar coins in the past is 58.22 euros.
- The coin has been auctioned 77 times, of which it has sold 71 times, indicating good demand.
- Previous hammer prices for coins with a similar condition (70) have varied, but there are examples of auctions reaching up to 90 euros.

3. Starting and Hammer Prices:
- The current starting price is 18 euros, which is quite low compared to the average hammer price.
- In previous auctions, coins with a condition of 70 have had hammer prices ranging from 20 to 90 euros.

4. Recent Trends: In the most recent auctions, hammer prices for coins of similar condition have shown an increase, suggesting that demand may be growing.

Based on these factors, an estimated maximum purchase price for this coin could be in the range of 70 to 90 euros. This is based on the historical hammer prices for coins of similar condition and the trend of increasing prices. However, since the starting price is 18 euros, it is likely that the final hammer price will be closer to the lower end of this range, unless there is significant competition among bidders.