Based on the data provided, we can observe that the coin in question has had varying starting and final prices in previous auctions. The current condition of the coin is estimated at 30 (BC+).

The average starting price in previous auctions has been 158 euros, while the average final price has been 357.14 euros.

Considering that the coin will be auctioned in the upcoming days with a starting price of 90 euros, and taking into account the previous auction prices as well as the current condition, we could estimate a maximum purchase price around 250-300 euros.

It is important to note that the final auction price may vary depending on the demand at that specific moment, so it is advisable to monitor the auction to adjust the offer accordingly.