Based on the data provided, we can see that the coin in question has had an average auction price of 99.89 euros in the past. Additionally, the current condition of the coin is 85 (VF+/XF-).

Considering that the current condition is quite good and the historical average auction price is 99.89 euros, we could estimate a maximum purchase price of around 110 euros. Since the coin will be auctioned soon, it is possible that the final auction price may be slightly higher than this estimated value.

Therefore, an estimated maximum purchase price for this coin at the upcoming auction could be around 110 euros.