Based on the data provided, we can observe that the coin in question has had varying starting and final prices in previous auctions, ranging from 15 euros to 125 euros. The estimated price has also fluctuated, with values ranging from 20 euros to 250 euros.

Given that the condition of the coin to be auctioned soon is 20 (BC-), we can infer that its state is not the best, which may influence the final auction price.

Considering the previous prices of this coin and taking into account its current condition, as well as the fact that it will be auctioned in the coming days, we could estimate a maximum purchase price of around 90 euros. It is important to note that this is just an estimate and the final auction price may vary depending on various factors such as demand at the auction and the interest of the buyers present.