Based on the provided data, we can observe that the coin in question has a grade of 30 (BC+), indicating that it is not in the best condition, but it is not the worst either. Additionally, it has been auctioned in the past on several occasions, with varying starting and final prices.

The starting price for the upcoming auction is 60 euros, and the historical average starting price is 130 euros, with an average final price of 170 euros. We can also see that in the last auction, the estimated price was 100 euros, but the final price was 60 euros.

Taking these data points into consideration, as well as previous prices for the coin, we could estimate a maximum purchase price around 120-150 euros. Given that the coin is not in the best condition and the final price in the last auction was lower than the starting price, it is advisable to be cautious when setting a maximum purchase price.