To estimate a maximum purchase price for the coin in question, we will consider several factors:

1. Coin Condition: The coin has a condition rating of 85 (MBC+/EBC-), indicating that it is in quite good shape. This generally translates to a higher price compared to coins with lower conditions.

2. Current Price and Previous Prices: The current starting price is 90 euros. In previous auctions, the highest hammer price for coins of similar condition has been 290 euros, although this may be an exceptional case. Most hammer prices for coins in the condition range of 70 to 90 have been between 35 and 141 euros.

3. Price Trends: The average hammer price for similar coins is 71.74 euros, suggesting that the hammer price may be below the current starting price.

4. Supply and Demand: The coin has been auctioned 53 times in the past, of which 41 have been successful sales. This indicates relatively good demand, which may influence the price.

5. Proximity of the Auction: Since it will be auctioned in the coming days, the urgency may influence the price that buyers are willing to pay.

Taking all these factors into account, an estimated maximum purchase price could be in the range of 120 to 150 euros. This range considers the good condition of the coin and the price trends in previous auctions, but it also takes into account that the starting price is 90 euros and that the average hammer price is significantly lower.