Based on the data provided, we can observe that the coin in question has had an average auction closing price of 388.1 euros in previous auctions. Additionally, its current condition is graded at 75 (MBC).

Considering that the starting price in the upcoming auction is 400 euros and the historical average closing price is 388.1 euros, we could estimate a maximum purchase price around that value. However, taking into account that the coin's condition is graded at 75 (MBC), which may slightly affect its value, we could adjust that estimated maximum price to around 380-390 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 its evolution to adjust the offer accordingly.