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

1. Condition: The coin has a condition of 70 (VF-), indicating that it is in quite good shape. This generally suggests that the final price could be higher than the average for coins in worse conditions.

2. Auction History:
- It has been auctioned 6 times in the past, of which it has sold 3 times.
- The average starting price is 9.83 euros, and the average final price is 8.67 euros.
- The starting and final prices in previous auctions varied, but there are examples where the starting price has been as high as 18 euros and the estimated price reached 30 euros.

3. Price Trends:
- In previous auctions, final prices have ranged between 9 and 14 euros, with an estimated price of up to 30 euros in one previous auction.
- Given that the coin has a condition of 70, it is reasonable to assume that it could achieve a final price higher than average.

4. Estimation:
- Considering the current starting price of 1 euro, which is quite low compared to previous starting prices, and the history of final prices, a reasonable maximum purchase price could be in the range of 15 to 20 euros, as this aligns with previous final prices for coins in similar conditions.

Therefore, an estimated maximum purchase price for this coin could be 20 euros.