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

1. Current condition: The coin has a condition of 70 (VF-), indicating that it is in an acceptable state, but not of the highest quality.

2. Auction history:
- The coin has been auctioned 6 times in the past, of which it has sold 5 times.
- The average starting price in previous auctions is 41.83 euros, and the average hammer price is 78.2 euros.
- Previous hammer prices for similar conditions (70) have been 40 euros (2020-11-19) and 50 euros (2023-01-18).

3. Price trends:
- In the auction on 2020-10-21, a coin with a condition of 85 sold for 146 euros, indicating that the price can increase significantly with better condition.
- In the auction on 2014-10-29, the hammer price was 130 euros, but the condition is not specified.

4. Current starting price: The starting price is 18 euros, which is relatively low compared to previous hammer prices.

Given that the condition of the coin is 70 and considering the previous hammer prices for similar conditions, an estimated maximum purchase price could be in the range of 50 to 70 euros, taking into account that the highest hammer price for a condition of 70 was 50 euros in the most recent auction.

Therefore, an estimated maximum purchase price could be 70 euros.