Based on the data provided, we can observe that the coin in question has had widely varying final prices throughout previous auctions. The starting price for the next auction is 70 euros, and the condition of the coin is rated at 70 (MBC-).

Given that the average final price has been 579.19 euros, and considering that the current condition of the coin is relatively good (70), we could estimate a maximum purchase price around that value. However, considering that the starting price is 70 euros, it is possible that the final auction price may be lower than the historical average.

Therefore, my estimation for the maximum purchase price of this coin in the next auction would be around 500 euros. It is important to note that auction prices can vary depending on demand and other factors, so it is advisable to monitor the auction and adjust the offer accordingly.