Based on the data provided, we can observe that the coin has had an average auction closing price of 52.17 euros in previous auctions. Additionally, the current condition of the coin is 85 (ebc-).

Considering that the starting price in the upcoming auction is 20 euros and the historical average closing price is 52.17 euros, we can estimate a maximum purchase price based on this data.

Given that the coin is in fairly good condition (85 ebc-) and considering its strong performance in previous auctions, we could consider a maximum purchase price around 60-70 euros.

It is important to note that the final auction price may vary depending on the demand at that specific time, but this estimation gives us a general idea of the price range we could aim to acquire the coin.