Based on the provided data, we can observe that the coin in question has had a starting price in this auction of 150 euros, with a conservation grade of 20 (BC-). Additionally, it has been auctioned in the past on five occasions, selling each time.

The previous prices of this coin in previous auctions have varied, with an estimated higher price of 1000 euros in a 2019 auction and a highest closing price of 650 euros in the same auction. The conservation grade of the coin in that auction was 85.

Considering these historical data and the current starting price, as well as the conservation grade of the coin in this auction (20 - BC-), we could estimate a maximum purchase price around 400-500 euros. It is important to note that the conservation grade of the coin can significantly influence its final value, so it is advisable to take this factor into account when estimating a price.