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

1. Starting price: 1500 euros.
2. Average auction price in the past: 2600 euros.
3. Condition of the coin: 85 (MBC+/EBC-), which is a fairly good condition.
4. Auction history: It has been auctioned once before, with an estimated price of 2000 euros and a hammer price of 2600 euros.

Given that the average hammer price in the past has been 2600 euros and considering that the condition is good (85), it is reasonable to think that the hammer price could be in a similar range or even higher, depending on the demand in the current auction.

Since the starting price is 1500 euros, which is quite attractive, and considering that there have been no failed sale attempts, it can be estimated that the interest in the coin is high.

Estimation of the maximum purchase price: We could consider a maximum purchase price that is in the range of the previous average hammer price, adjusted for the condition and current demand.

Therefore, an estimated maximum purchase price could be between 2500 and 2800 euros. This is based on the previous average hammer price and the good condition of the coin.