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: 3400 euros.
3. Condition of the coin: 100 (Uncirculated), indicating that it is in excellent condition.
4. Auction history: It has been auctioned once before, with a hammer price of 3400 euros.

Given that the coin has a high condition rating (100) and has reached a hammer price of 3400 euros in the past, it is reasonable to consider that the hammer price could be in a similar range or even higher, depending on the demand in the current auction.

Estimation of the maximum purchase price:
- Since the average hammer price has been 3400 euros and considering that the coin will be auctioned again, a maximum purchase price could be between 3400 and 3600 euros, assuming that demand remains stable or increases.

Therefore, an estimated maximum purchase price could be 3600 euros.