Based on the data provided, we can observe that the coin in question has had closing prices ranging from 49.92 euros to 1926.54 euros in previous auctions. The condition of the coin this time is described as "70 (MBC-)", indicating a medium to low conservation state.

Given that the average closing price in previous auctions has been 340 euros and the starting price this time is 40 euros, we can consider that the estimated maximum purchase price could be around the historical average closing price. However, considering the medium to low conservation of the coin this time, the final closing price may be affected.

Taking all these factors into consideration, an estimated maximum purchase price for this coin in the upcoming auction could be around 300-350 euros. It is important to note that in previous auctions, the closing price has sometimes exceeded the estimated price, so it is advisable to monitor the auction's progress to adjust the offer accordingly.