To estimate a maximum purchase price for the coin in question, we can analyze the provided data, including the starting price, the current grade, and the hammer prices from previous auctions.

1. Grade: The coin has a grade of 70 (MS-). This is an important factor, as coins in better condition tend to achieve higher prices at auctions.

2. Previous hammer prices: By looking at the hammer prices of coins with similar grades (75 and 85), we can see that they have reached hammer prices that vary considerably. For example:
- In 2014, a coin with a grade of 85 was sold for 532.22 euros.
- In 2016, a coin with a grade of 75 was sold for 340 euros.
- In 2023, a coin with a grade of 75 was sold for 360 euros.

3. Average hammer price: The average hammer price for this coin is 687.53 euros, indicating that, in general, coins of this reference tend to reach higher prices.

4. Starting price: The current starting price is 180 euros, which is significantly lower than the average hammer price.

5. Sales trends: Out of the 20 times it has been auctioned, 16 have been sold, indicating good demand for this coin.

Based on these factors, an estimated maximum purchase price could be in the range of 300 to 500 euros, considering that the grade is slightly lower than the coins that have reached higher prices, but there is still significant potential for appreciation.

Therefore, a reasonable maximum purchase price could be 450 euros.