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

1. Coin Condition: The coin to be auctioned has a condition of 75 (MS), indicating that it is in quite good shape. This is important because coins in better condition tend to fetch higher prices.

2. Previous Auction Prices: By looking at the hammer prices from previous auctions for coins with similar conditions:
- In 2022, a coin with a condition of 75 sold for 170 euros.
- In 2021, a coin with a condition of 70 sold for 180 euros.
- In 2022, another coin with a condition of 80 sold for 260 euros.

3. Average Hammer Price: The average hammer price for previous auctions is 251.67 euros, suggesting that, in general, coins of this reference tend to reach higher prices.

4. Starting Price and Average Starting Price: The current starting price is 175 euros, and the average starting price in previous auctions is 180 euros. This indicates that the starting price is reasonable and could attract bidders.

5. Auction Trends: Since the coin has sold in 6 out of the last 7 auctions, there is good demand for this reference.

Based on these factors, an estimated maximum purchase price could be between 220 and 260 euros, considering that the condition is good and that the average hammer price in the past has been above 250 euros. Therefore, a reasonable maximum purchase price could be 250 euros.