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

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

2. Previous Prices: By looking at previous auction prices for coins with similar conditions (EF or close), we can see that auction prices have varied. For example:
- In previous auctions, coins with a condition of 85 have sold for around 85-150 euros.
- Coins with a condition of 90 have reached auction prices of up to 270 euros.

3. Starting Price and Average Hammer Price: The current starting price is 200 euros, and the average hammer price for this coin in the past has been 86.06 euros. However, given that the condition is high, it is reasonable to expect that the hammer price will be above the average.

4. Auction Trends: The coin has been auctioned 106 times, with a sell-through rate of 91.5%. This suggests that there is consistent interest in this coin, which may increase its value at auction.

Based on these factors, an estimated maximum purchase price for this coin could be between 250 and 300 euros, considering its good condition and market interest. This would allow a competitive buyer at the auction, given the historical hammer prices for similar coins.