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

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

2. Previous Auction Prices: By observing the hammer prices of coins with similar grades (70 and 80), we can see that the hammer prices have varied. For example:
- In previous auctions, coins with a grade of 70 have reached hammer prices of 170, 160, and 200 euros.
- Coins with a grade of 80 have reached hammer prices of 260, 320, and 390 euros.

3. Average Hammer Price: The average hammer price for this coin is 335.81 euros, indicating that, in general, coins of this reference tend to sell for relatively high prices.

4. Starting Price and Average Starting Price: The current starting price is 75 euros, and the average starting price in the past has been 166.5 euros. This suggests that the current starting price is quite low compared to the historical average.

5. Recent Trends: In the most recent auctions, the hammer price has been 320 euros for a coin with a grade of 75, indicating that there is significant interest and value in coins of similar quality.

### Estimation of Maximum Purchase Price
Taking all these factors into account, an estimated maximum purchase price for the coin with a grade of 70 could be between 200 and 300 euros. This is based on the analysis of previous hammer prices and the price trend in recent auctions.

Therefore, a reasonable maximum purchase price could be 250 euros. This allows for some margin for competition in the auction, given that the starting price is relatively low.