Based on the data provided, we can observe that the coin in question has had an average starting price of 34.75 euros in previous auctions, with a median closing price of 27.5 euros. Additionally, the current condition of the coin is graded at 90 (EBC), indicating that it is in fairly good condition.

Regarding the previous prices of this coin in past auctions, we can see the following values:

- In the auction on September 13, 2013, the coin had a starting price of 32 euros and a condition grade of 75.
- In the auction on September 12, 2014, the coin had a starting price of 32 euros and a closing price of 40 euros, with a condition grade of 75.
- In the auction on May 30, 2018, the coin had a starting price of 15 euros, an estimated price of 25 euros, and a closing price of 15 euros, with a condition grade of 75.

Given that the coin is in a condition grade of 90 (EBC) and has had previous starting prices ranging from 15 to 32 euros, we could estimate a maximum purchase price around 35-40 euros, considering the median closing price of 27.5 euros and the good condition of the coin. However, please note that the final price at auction may vary depending on demand and other factors.