Based on the data provided, we can observe that the coin in question has had a starting price in the current auction of 275 euros and is in a conservation grade of 70 (MBC-). Additionally, it has been auctioned in the past on several occasions, with closing prices ranging between 150 and 1500 euros.

The average closing price of this coin in previous auctions has been 474.11 euros, with an average starting price of 344.26 euros. Considering the current conservation grade is 70 (MBC-), we can estimate that the closing price of this coin in the current auction could be around 474.11 euros.

Given that the starting price is 275 euros and taking into account the upward trend in previous closing prices, as well as the demand for this coin (considering it has sold in a high percentage of past auctions), we could estimate a maximum purchase price of around 500 euros.

Therefore, my estimation of the maximum purchase price for this coin in the current auction would be around 500 euros.