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. Auction History:
- The average hammer price in the past has been 74.49 euros.
- It has been auctioned 66 times, of which 45 have been sales, indicating a consistent interest in this coin.
- In previous auctions, hammer prices of up to 459.61 euros have been reached for coins with a similar condition (90).

3. Recent Starting and Hammer Prices:
- In the most recent auction, the starting price was 50 euros, and the hammer price was 85 euros.
- In another recent auction, the starting price was 50 euros, and the estimated price was 100 euros.

4. Price Trends:
- Hammer prices have shown significant variations, with some reaching very high figures in similar conditions.

Based on these factors, an estimated maximum purchase price could be in the range of 85 to 120 euros, considering that the interest in the coin is high and its condition is good. However, given the hammer price history, a reasonable maximum purchase price could be 100 euros. This allows for competition in the auction and reflects the value of the coin in its current state.