Based on the provided data, we can conduct an analysis to estimate a maximum purchase price for the coin in question.

1. Starting price: 2500 euros.
2. Average hammer price in the past: 5000 euros.
3. Coin condition: 100 (Uncirculated), indicating it is in excellent condition.
4. Auction history: It has been auctioned once before, with an estimated price of 3000 euros and a hammer price of 5000 euros.

Given that the coin has a high condition rating (100) and has reached a hammer price of 5000 euros in the past, it is reasonable to consider that interest in this coin could be high in the upcoming auction.

Estimation of the maximum purchase price:
- Since the average hammer price has been 5000 euros and considering that the starting price is 2500 euros, a maximum purchase price could be in the range of 5000 to 6000 euros, depending on the demand at the auction.

Therefore, an estimated maximum purchase price could be 5500 euros. This allows for a margin for competition in the auction, given the price history and the high condition of the coin.