To estimate a maximum purchase price for the coin in question, we will consider several factors:

1. Current Condition: The coin is in a condition of 90 (EF), which indicates that it is in quite good shape. This generally translates to a higher price compared to coins in lower conditions.

2. Current Starting Price and Previous Prices: The current starting price is 450 euros. In previous auctions, we have seen hammer prices that vary, but there are examples of similar coins in comparable condition that have sold for significantly higher prices. For instance, in 2020, a coin with a condition of 95 sold for 550 euros, and in 2022, another with a condition of 95 was hammered at 700 euros.

3. Sales Trends: The coin has been auctioned 74 times, with a high percentage of sales (68 out of 74). This suggests that there is consistent interest in this coin, which may increase its value.

4. Average Hammer Price: The average hammer price for similar coins is 183.72 euros, but given that this coin's condition is superior, we can expect the hammer price to be higher.

5. Previous Estimates: In previous auctions, the estimated price for coins of similar condition has been up to 800 euros.

Taking all these factors into account, an estimated maximum purchase price for this coin could be between 600 and 750 euros, considering its good condition and market interest. However, given the starting price of 450 euros, it is likely that the hammer price will not exceed 700 euros in this specific auction.

Therefore, a reasonable maximum purchase price could be 700 euros.