Based on the data provided, we can observe that the coin in question has had an average auction closing price of 89.17 euros in previous auctions. Additionally, its current condition is graded at 70 (MBC-), indicating that it is in an acceptable but not excellent condition.

Considering that the average closing price has been 89.17 euros and the current condition is 70, we can estimate a maximum purchase price for this coin in the upcoming auction. Given the relatively good condition and the close average closing price to 90 euros, we could consider a maximum purchase price around 100 euros.

However, it is important to note that the starting price this time is 50 euros, so the final closing price may be lower than estimated. Nevertheless, a maximum purchase price of around 100 euros seems reasonable given the circumstances.