To estimate a maximum purchase price for the coin in question, we can consider several factors based on the provided data:

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

2. Previous Prices: By looking at previous auction prices for coins with a similar condition (90), we can see that they have reached hammer prices of up to 340 euros in recent auctions. For example, at the auction on March 16, 2023, a coin with a condition of 95 was sold for 340 euros.

3. Starting Price and Average Hammer Price: The current starting price is 225 euros, and the average hammer price in the past has been 188.56 euros. This suggests that the starting price is reasonable, but it also indicates that the hammer price may be lower than the starting price.

4. Auction Trends: The coin has been auctioned 55 times, with a 76% sell-through rate (42 out of 55). This suggests that there is consistent interest in this coin, which may influence its price.

5. Price Estimates: In previous auctions, estimated prices for coins of similar condition have varied, but some have reached up to 400 euros. However, it is important to be conservative in the estimation.

Taking all these factors into account, an estimated maximum purchase price for this coin could be around 300-350 euros. This is based on the condition, previous hammer prices, and general interest in the coin.