To estimate a maximum purchase price for the coin that will be auctioned, we can consider several factors:

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

2. Historical auction data:
- The average hammer price for similar coins in the past has been 456.44 euros.
- The last auction of a coin with a similar condition (90) had a hammer price of 650 euros in 2022.
- In previous auctions, hammer prices for coins with conditions ranging from 80 to 90 have fluctuated between 350 and 650 euros.

3. Starting price and estimates:
- The starting price of the auction is 500 euros, which is a reasonable starting point.
- The estimated price for this auction is 600 euros, suggesting that bidders may be willing to pay more.

4. Sales trends: The coin has been sold in 36 out of the 39 previous auctions, indicating good demand.

Based on these factors, an estimated maximum purchase price could be around 650 euros, as this is a price that has been reached in previous auctions for coins of similar condition and aligns with the estimated price of 600 euros. However, it is important to consider that the market can fluctuate, and competition in the auction may influence the final price.