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

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

2. Auction History:
- In the past, the coin has been auctioned 5 times and has sold in all of them, indicating a consistent interest in the coin.
- The previous hammer prices are:
- €750 (with a condition of 85)
- €500 (with unspecified condition)
- €566 (with a condition of 80)
- €900 (with a condition of 85)
- The average hammer price is €683.2, suggesting that, in general, buyers are willing to pay around this figure.

3. Starting Price and Estimates:
- The current starting price is €600, which is consistent with the average starting price in previous auctions.
- The estimated price for this auction is €1000, indicating that there are expectations for the coin to reach a higher price, although this may depend on demand at the time of the auction.

4. Condition Comparison:
- The condition of 70 is lower than the conditions of 80 and 85 from previous auctions, which could limit the maximum price that could be reached in this auction.

Taking all these factors into account, an estimated maximum purchase price could be in the range of €600 to €750, considering that the current condition is lower than the coins that have sold for higher prices. A hammer price around €700 could be a reasonable target, given the sales history and current condition.

Therefore, an estimated maximum purchase price could be €700.