Based on the provided data, we can see that the coin in question has a conservation grade of 75 (MBC) and has had varying starting and estimated prices in previous auctions. The starting price for the upcoming auction is 18 euros, and the average auction closing price in previous auctions has been 112.5 euros.

Considering that the average starting price in previous auctions has been 89.5 euros and the highest estimated price was 200 euros, we can estimate a maximum purchase price for this coin in the upcoming auction.

Given that the coin is in a conservation grade of 75 (MBC) and has had previous estimated prices of up to 200 euros, we could consider a maximum purchase price in the range of 150 to 200 euros, taking into account the fluctuation of previous prices and the conservation of the coin.

Therefore, an estimated maximum purchase price for this coin in the upcoming auction could be around 150 to 200 euros.