To estimate a maximum purchase price for the coin in question, we can consider 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. Current Starting Price and Previous Prices: The current starting price is 600 euros. In previous auctions, the average hammer price has been 678.48 euros, indicating that coins of this reference usually sell for above the starting price.

3. Sales History: The coin has been auctioned 58 times, of which 56 have been successful sales. This suggests a good demand for this coin.

4. Previous Hammer Prices: Looking at previous hammer prices for coins with similar conditions, we can see that they have reached prices of up to 1300 euros in optimal conditions. However, given that the condition of this coin is 70, it is reasonable to expect that the hammer price will be below that range.

5. Price Estimates: In recent auctions, coins with similar conditions have had hammer prices ranging from 550 to 850 euros.

Taking all these factors into account, an estimated maximum purchase price for this coin could be around 800-900 euros, considering that the condition is a limiting factor and that the average hammer price is 678.48 euros.

Therefore, a reasonable maximum purchase price could be 850 euros.