Based on the data provided, we can observe that the coin in question has had an average auction price of 186.77 euros in previous auctions. Additionally, its current condition is 85 (ebc-).

Considering that the coin will be auctioned in the coming days with a starting price of 90 euros, we can estimate a maximum purchase price based on the previous average auction price and the current condition. Given that the condition is quite good (85), and considering that the average auction price has been 186.77 euros, we could consider a maximum purchase price around 200-220 euros.

It is important to note that the final auction price will depend on the demand at that specific moment, so it is advisable to monitor the auction's progress to adjust the offer accordingly.