To estimate a maximum purchase price for the coin in question, we can analyze the provided data and 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. Previous Auction Prices:
- Previous hammer prices for coins with similar conditions (70 and 80) range between 150 and 190 euros.
- The average hammer price for coins in condition 70 has been approximately 170 euros.

3. Starting Price and Average Hammer Price:
- The current starting price is 140 euros, which is reasonable compared to the average hammer price of 159.27 euros.
- The average starting price of 145.83 euros also suggests that the current starting price is competitive.

4. Sales Trends: The coin has been auctioned 13 times, of which 12 have been sold. This indicates good demand and a history of successful sales.

5. Previous Estimates: In previous auctions, the estimated price has been significantly higher than the current starting price, suggesting that there could be potential for an increase in the hammer price.

Based on these factors, an estimated maximum purchase price could be around 170-180 euros, considering that the average hammer price for similar conditions has been 170 euros and that there is a history of hammer prices exceeding the current starting price.

Therefore, a reasonable maximum purchase price could be 180 euros.