Based on the provided data, we can see that the coin in question has a grade of 30 (BC+), with a starting price in the last auction of 70 euros and an estimated price of 90 euros. The average starting price for this coin is 47.5 euros, and the average closing price is 35 euros.

Considering that the coin has been auctioned twice in the past, sold once and not sold on another occasion, we can see that there is interest in it. However, with a grade of 30 (BC+), which is not the best, its price is likely to be affected.

Given that the estimated price in the last auction was 90 euros and the average closing price is 35 euros, we could consider a maximum estimated purchase price around 70-80 euros, taking into account the coin's grade and historical auction data. It is important to note that the final price will depend on the demand at the auction and other factors that may influence potential buyers' decisions.