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

1. Starting price: 600 euros.
2. Average hammer price in the past: 5000 euros. This indicates that, although the starting price is relatively low, the interest in the coin may be high, suggesting it could reach a much higher price at auction.
3. Condition: The coin has a condition rating of 70 (VF-), which is a good condition, although not the best. This may influence the price, as coins in better condition tend to fetch higher prices.
4. Auction history: It has been auctioned once and sold on that occasion, indicating there is demand for this coin.

Given that the average hammer price is significantly higher than the starting price, and considering the good condition of the coin, an estimated maximum purchase price could be in the range of 4000 to 6000 euros. This is based on the potential interest from collectors and the history of hammer prices.

Therefore, an estimated maximum purchase price could be around 5000 euros.