Based on the data provided, we can observe that the coin in question has had an average auction closing price of 183.39 euros in previous auctions. Additionally, its current condition is 80 (MBC+).

Considering that the coin will be auctioned in the upcoming days with a starting price of 90 euros, we can estimate a maximum purchase price based on the historical average auction closing price and the current condition. Given that the condition is good but not excellent, and considering that the average auction closing price has been 183.39 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.