To estimate a maximum purchase price for the coin in question, we will consider several factors:

1. Current Condition: The coin has a condition of 70 (VF-). This is an important factor, as coins in better condition tend to reach higher prices.

2. Auction History:
- The coin has been auctioned 6 times and has sold on all occasions, indicating a consistent interest in the coin.
- The average hammer price in previous auctions is 1733.33 euros, which provides a good reference.

3. Previous Prices:
- In previous auctions, hammer prices have varied, but there are examples of hammer prices exceeding 2000 euros, especially in higher conditions (like 85).
- The most recent auction with a condition of 70 had a hammer price of 1000 euros, indicating that this level of condition may limit the price.

4. Starting Price and Estimates:
- The current starting price is 1500 euros, which is reasonable given the price history.
- The estimated price of 2000 euros in the 2020 auction suggests that, under optimal conditions, the coin could reach that range, but the current condition may limit it.

Based on these factors, an estimated maximum purchase price could be between 1700 and 2000 euros, considering that the condition of 70 may bring the price closer to the lower end of this range. Therefore, a reasonable maximum purchase price could be 1800 euros.