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. Auction History:
- The average hammer price for similar coins is 91.9 euros.
- In the past, coins with similar conditions (around 90) have sold for varying prices, but some examples are:
- 2024-01-18: 160 euros (condition 95)
- 2024-12-18: 150 euros (condition 95)
- 2022-10-19: 65 euros (condition 95)
- 2022-12-14: 90 euros (condition 90)

3. Starting Price and Average Starting Price: The current starting price is 20 euros, and the average starting price is 57.7 euros. This suggests that the starting price is relatively low compared to the market value.

4. Sales Trends: The coin has been sold in 32 out of 40 auctions, indicating good demand.

5. Comparison with Previous Prices: By looking at previous hammer prices for coins with similar conditions, we can see that prices have reached up to 160 euros for coins in better condition.

### Maximum Purchase Price Estimate
Given that the coin has a condition rating of 90 and considering the hammer price history, a reasonable maximum purchase price could be in the range of 100 to 150 euros. This is based on the fact that coins in similar conditions have reached hammer prices of up to 160 euros, and the average hammer price is 91.9 euros.

Therefore, an estimated maximum purchase price could be around 120 euros. This provides a margin to compete in the auction without exceeding the observed market value.