To estimate a maximum purchase price for the coin in question, let's consider the following factors:

1. Starting price: 45,000 euros.
2. Current condition: 90 (EBC), which is good condition, although lower than the 95 condition of the previous auction.
3. Average hammer price in the past: 85,000 euros, which is a good indicator of market value.
4. Auction history: The coin has been auctioned once before, with an estimated price of 30,000 euros and a hammer price of 85,000 euros.

Since the current condition is slightly lower than that of the previous auction, it is reasonable to adjust the expected hammer price. However, interest in the coin seems to be high, given that there have been no failed sale attempts.

Taking these factors into account, a maximum purchase price could be set in a range between the previous average hammer price and the current starting price.

Estimated maximum purchase price: It may be reasonable to consider a maximum purchase price of around 75,000 to 80,000 euros, given that the condition is slightly lower than the previous one, but still good interest is expected in the auction.