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

1. Current condition: The coin has a condition of 70 (VF-), indicating that it is in an acceptable state, but not excellent. This suggests that its value will be lower than that of coins in better condition.

2. Auction history:
- It has been auctioned 9 times, of which it has sold 8 times. This indicates good demand.
- The average starting price in previous auctions is 407.14 euros, and the average hammer price is 661.43 euros. This suggests that, in general, coins of this reference tend to sell for a considerably higher price than their starting price.

3. Previous prices:
- The hammer prices of coins with similar conditions (75-90) have varied, but they have sold for prices ranging from 400 to 1400 euros, depending on the condition.
- The last auction with a condition of 80 had a hammer price of 400 euros, while one with a condition of 90 sold for 650 euros.

4. Current starting price: The starting price is 150 euros, which is quite low compared to previous hammer prices.

Given that the condition of the coin is 70, and considering the hammer price history, an estimated maximum purchase price could be in the range of 300 to 450 euros. This is based on the fact that, although the condition is not the best, the interest in the coin and the sales history suggest that it could reach a reasonable price.

Therefore, an estimated maximum purchase price could be approximately 400 euros.