Based on the data provided, we can observe that the coin in question has had an average auction closing price of 21.8 euros in previous auctions. Additionally, the condition of this coin has been described as '75 (VF).'

Considering that the condition of the coin is 75 (VF) and the average closing price has been 21.8 euros, we can estimate a maximum purchase price around that value or slightly higher, taking into account the trend of previous prices.

Therefore, an estimated maximum purchase price for this coin in the upcoming auction could be around 22-23 euros. It is important to note that this is just an estimate and the final price could vary depending on demand at the auction.