To estimate a maximum purchase price for the coin in question, we can analyze the provided data:

1. Starting price: 850 euros.
2. Coin condition: 70 (MBC-), indicating a fairly good condition.
3. Auction history:
- It has been auctioned 8 times, of which it has sold 6 times.
- The average hammer price in previous auctions is 518.1 euros, but it should be noted that the current starting price is significantly higher.
- In previous auctions, hammer prices have varied, with a maximum price of 1172.41 euros in 2015 for a coin with similar condition (75).

4. Price trends:
- The general trend seems to be that hammer prices have been increasing, especially for coins in good condition.
- The last auction with a hammer price of 1172.41 euros suggests that there is a market willing to pay high prices for well-preserved coins.

Given that the condition of the current coin is 70 (MBC-), which is lower than the condition of 75 from the highest auction, but still represents good condition, we can estimate a maximum purchase price.

Estimation of the maximum purchase price:
- Considering the starting price of 850 euros and the history of hammer prices, a reasonable maximum purchase price could be in the range of 900 to 1100 euros, depending on the demand at the auction.

Therefore, an estimated maximum purchase price could be approximately 1000 euros.