Given that the coin has a conservation rating of 90 (EBC - Excellent Good Conservation) and has not been auctioned or sold in the past, the starting price of 900 euros seems reasonable. However, since there are no historical sales data for this reference, it is difficult to establish an exact hammer price.

In general, coins in good condition (EBC) can reach hammer prices ranging from 80% to 120% of the starting price, depending on demand and collector interest.

Since the starting price is 900 euros, an estimated maximum purchase price could be in the range of 1,080 euros (120% of the starting price) if there is considerable interest in the coin.

Therefore, an estimated maximum purchase price could be approximately 1,080 euros.