To estimate a maximum purchase price for the coin in question, we can 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. Auction History:
- The average hammer price for this coin in the past is 40.13 euros.
- Hammer prices of up to 240 euros have been recorded for coins in better condition (100) and lower prices for lesser conditions (80 and 95).

3. Price Trends:
- In recent auctions, hammer prices of 45 euros have been seen for coins in condition 95 and 140 euros for a coin in condition 100.
- The current starting price is 12 euros, suggesting that there is considerable room for the hammer price to be higher.

4. Comparison with Previous Prices:
- In the most recent auction of this coin, the hammer price was 25 euros with a condition of 90, which may be a good indicator of what can be expected.

Taking all these factors into account, an estimated maximum purchase price for the coin in condition 90 could be between 50 and 70 euros, considering that the average hammer price is 40.13 euros and that there are examples of higher prices in similar conditions.

Therefore, a reasonable maximum purchase price could be 70 euros.