Based on the data provided, we can observe that the coin in question has had an average auction price of 25.93 euros in previous auctions. Additionally, its condition has been described as '80 (MBC+)'.

Considering that the condition is good and the average auction price has been 25.93 euros, we could estimate a maximum purchase price around that value or slightly higher, taking into account that the starting price in this auction is 18 euros.

Therefore, an estimated maximum purchase price for this coin in the next auction could be around 26-28 euros. It is important to note that this is just an estimate and the final price will depend on demand and other factors in the auction.