Based on the provided data, we know that the coin is in a condition of 70 (MBC-), has been auctioned once in the past, and was sold on that occasion. The average auction price in the previous auction was 90 euros, with a starting price of 25 euros.

Given that the coin is in an acceptable condition (70), has had good demand in previous auctions, and was sold in its only past auction, we could expect the auction price in a new auction to be in a similar range or even higher than the previous average auction price.

Considering these factors, and taking into account that the starting price is 25 euros, we could estimate a maximum purchase price of around 100-110 euros for this coin in the next auction. It is important to note that the final price will depend on the demand in the specific auction and other factors that may influence collectors' valuation at that time.