Based on the data provided, we can observe that the coin in question has had an average auction closing price of 70.63 euros in previous auctions. Additionally, its condition has been described as 70 (MBC-), indicating a medium to low conservation state.

Taking into account the previous prices of the coin in past auctions, as well as its current condition, we can estimate a maximum purchase price. Given that the average closing price has been 70.63 euros and the current condition is 70 (MBC-), we could consider an estimated maximum purchase price around 75-80 euros.

It is important to note that the starting price in the upcoming auction is 18 euros, so the final closing price may end up above this figure. However, please keep in mind that this is just an estimation and the final price may vary depending on the demand at the auction and other factors.