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

1. Current Condition: The coin has a condition of 70 (VF-), indicating that it is in an acceptable state, but not of the highest quality.

2. Auction History:
- The average hammer price for similar coins has been 669.28 euros.
- In the past, coins with similar conditions (around 70) have sold for prices that varied considerably, but some relevant examples are:
- In 2011, a coin with a condition of 75 sold for 210 euros.
- In 2013, another coin with a condition of 75 sold for 120 euros.
- In 2016, a coin with a condition of 75 sold for 372.1 euros.
- In 2021, a coin with a condition of 70 sold for 190 euros.

3. Starting Price and Average Starting Price:
- The current starting price is 150 euros, which is quite low compared to the average hammer price of 669.28 euros.
- The average starting price of 375.41 euros also suggests that there is potential for an increase in the hammer price.

4. Recent Trends:
- In recent auctions, hammer prices have shown a trend of being higher, especially for coins in good condition.

Based on these factors, an estimated maximum purchase price could be in the range of 300 to 500 euros. This is based on the historical hammer prices for coins of similar condition and the potential for an increase in the hammer price depending on demand and collector interest.

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