Based on the provided data, we can see that the coin in question has had previous auction starting prices of €60 and €12, with estimated prices of €90 and €20 respectively. The final auction prices were €80 and €27. The coin's condition has been described as "30 (BC+)".

Given that the coin will be auctioned with a starting price of €9 and considering that the average starting price in the past was €27, we could estimate a maximum purchase price based on the previous average final auction price, which was €46.

Taking into account the coin's condition and its price history, an estimated maximum purchase price for this coin in the upcoming auction could be around €40-50. It is important to note that the final price will depend on the demand at the auction and other factors that may influence potential buyers' decisions.