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

1. Current Condition: The coin has a condition of 90 (EF), which indicates that it is in 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, we can see that:
- In 2020, a coin with a condition of 85 was auctioned for 90 euros.
- In 2022, a coin with a condition of 85 was auctioned for 95 euros.
- In 2023, a coin with a condition of 90 was auctioned for 110 euros.

3. Average Auction Price: The average auction price for this coin is 111.76 euros, suggesting that the market is willing to pay close to this amount for coins in similar conditions.

4. Starting Price: The starting price is 90 euros, which may influence the perception of the coin's value.

5. Auction Trends: The coin has been auctioned 28 times, of which 22 have sold. This indicates a consistent interest in the coin, which may increase its value.

Taking all these factors into account, an estimated maximum purchase price for this coin could be between 120 and 140 euros. This is based on the current condition, previous auction prices, and general interest in the coin.