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

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

2. Auction History:
- The coin has been auctioned 11 times, of which it has sold 9 times. This indicates good demand.
- The average hammer price in previous auctions is 297.22 euros, suggesting that, in general, coins of this reference tend to sell for relatively high prices.

3. Previous Prices:
- Looking at previous hammer prices, we can see that they have varied considerably, from 135 euros to 700 euros, depending on the condition and other factors.
- The last auction in which a coin with a similar condition (70) was sold had a hammer price of 210 euros.

4. Starting Price and Average Starting Price:
- The current starting price is 100 euros, which is quite low compared to the average hammer price of 297.22 euros.

5. Price Trends:
- Since the average hammer price is significantly higher than the starting price, this suggests that there is potential for the coin to sell for a higher price.

Based on these factors, an estimated maximum purchase price could be in the range of 250 to 300 euros, considering that the condition is 70 and that the price history shows that coins in similar conditions have reached hammer prices in that range.

Therefore, a reasonable maximum purchase price could be approximately 280 euros.