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 acceptable condition, but not among the best. This can influence the price, as coins in better condition typically fetch higher prices.

2. Auction History:
- The average starting price from previous auctions is 14.18 euros, and the average hammer price is 16.4 euros.
- In past auctions, hammer prices have varied, but there are examples where the coin has sold for 18 euros in similar conditions.

3. Price Trends:
- In previous auctions, estimated prices have ranged between 15 and 30 euros, depending on condition and other factors.
- The last auction had a starting price of 12 euros and an estimated price of 20 euros, suggesting there is interest in this coin.

4. Supply and Demand: Since it has been auctioned 10 times and sold 6 times, there is moderate interest in the coin, which can influence the price.

Based on these factors, an estimated maximum purchase price could be around 20-25 euros, considering that the average hammer price is 16.4 euros and that estimated prices in previous auctions have reached up to 30 euros.

Therefore, a reasonable maximum purchase price could be 25 euros.