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), indicating that it is in good shape. This generally translates to a higher price compared to coins in lower conditions.

2. Starting Price and Average Hammer Price: The starting price is 75 euros, and the average hammer price in previous auctions is 80.86 euros. This suggests that the hammer price tends to be above the starting price.

3. Auction History: The coin has been auctioned 37 times, of which it has sold 23 times. This indicates good demand. Additionally, the highest recorded hammer price in the past was 200 euros, although this occurred in an auction with a condition of 110.

4. Recent Trends: In the most recent auction, the coin sold for 85 euros with a condition of 90, which is a good indicator that the price could remain in a similar range.

5. Comparison with Previous Prices: Looking at previous hammer prices for coins with similar conditions, the range seems to be between 70 and 200 euros, but most sales have occurred in a lower range.

Taking all these factors into account, an estimated maximum purchase price for this coin could be around 100-120 euros. This is based on the good condition, historical demand, and recent auction behavior.