Based on the data provided, we can observe that the coin in question has had a starting price in the current auction of 18 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 28 and 410 euros.

The average closing price of this coin has been 113.59 euros, and the average starting price has been 67.21 euros. Considering the current conservation grade is 70 (MBC-), we can assume that the estimated purchase price could fall within an intermediate range.

Given that the highest closing price was 410 euros and the current starting price is 18 euros, we could estimate a maximum purchase price around 200 euros, considering the conservation grade and previous closing prices.

Therefore, my estimation of the maximum purchase price for this coin in the current auction would be around 200 euros.