Based on the data provided, we can observe that the coin in question has had starting prices ranging from 18 to 420 euros in previous auctions. The average selling price has been 81 euros, with a conservation value of 80 (MBC+).

Considering that the starting price in this auction is 40 euros and the average selling price has been 81 euros in the past, we could estimate a maximum purchase price around that value. However, taking into account that the conservation value of the coin is 80 (MBC+), indicating it is in good condition, we could consider a slightly higher maximum purchase price than the average selling price.

Therefore, an estimated maximum purchase price for this coin in the current auction could be around 85-90 euros. It is important to note that the final price will depend on the demand at the auction and other factors that may influence the decision of potential buyers.