Based on the provided data, we can observe that the coin in question has had an average auction price of 307.1 euros in the past. Additionally, its current condition is 90 (EBC).

Considering that the current condition is quite good and the average auction price has been 307.1 euros, we could estimate a maximum purchase price around 330-350 euros. However, please note that the starting price at the next auction is 350 euros, so it is possible that the final auction price may exceed this amount.

In summary, an estimated maximum purchase price for this coin could be around 330-350 euros, taking into account its auction history and current condition.