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

1. Condition of the coin: The coin to be auctioned has a condition rating of 90 (EBC), indicating that it is in quite good shape. This generally translates to a higher price compared to coins with lower conditions.

2. Historical data: By looking at previous auction prices for similar coins, we can see that the average hammer price is 144.45 euros. However, there have been auctions where significantly higher prices have been reached, such as in the 2014 auction where it sold for 850 euros with a condition rating of 95.

3. Starting price and average starting price: The starting price for this auction is 200 euros, which is above the average starting price of 89.53 euros. This suggests that the auction house has higher expectations for this particular coin.

4. Price trends: In recent auctions, hammer prices have shown a trend of increasing, especially for coins in good condition.

Taking all these factors into account, an estimated maximum purchase price could be in the range of 300 to 400 euros, considering that the condition is good and there are precedents for higher hammer prices in the past. However, given the starting price of 200 euros, it is possible that buyers may be willing to bid more, especially if there is interest in the coin.

Therefore, a reasonable maximum purchase price could be 350 euros.