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

1. Starting price: 450 euros.
2. Average hammer price in the past: 600 euros.
3. Coin condition: 100 (Uncirculated), indicating it is in excellent condition.
4. Historical data: In the previous auction, the coin was estimated at 1000 euros, but it sold for 600 euros.

Given that the coin has a high condition rating (100) and has had an average hammer price of 600 euros in the past, it is reasonable to consider that interest in this coin could be high, especially if it has sold well previously.

Taking these factors into account, an estimated maximum purchase price could be between the previous average hammer price (600 euros) and the previous estimated price (1000 euros). However, since the starting price is 450 euros, it is likely that bidders will be willing to pay a bit more.

Therefore, an estimated maximum purchase price could be approximately 800 euros. This reflects a reasonable interest in the coin, considering its condition and auction history.