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 is quite good, although lower than some coins that have been sold in the past with a condition of 95 or 100.

2. Historical Prices:
- The average hammer price from previous auctions is 3094.44 euros.
- Previous auctions with a condition of 95 have reached hammer prices of up to 6000 euros (in the case of the auction on 2022-03-17).
- The last auction with a condition of 95 had a hammer price of 4200 euros (2023-03-16).

3. Starting Price and Estimates:
- The current starting price is 2500 euros, which is a reasonable starting point.
- The estimated price for this auction is 3500 euros, indicating that the coin is expected to reach a price higher than the starting price.

4. Sales Trends:
- Out of the 13 times it has been auctioned, 11 have been sold, indicating good demand.

5. Comparison with Previous Prices:
- The condition of 90 is lower than the conditions of 95 and 100 that have reached higher prices, so the hammer price should not significantly exceed 4200 euros.

Taking all these factors into account, an estimated maximum purchase price for this coin could be around 3800-4000 euros. This is based on the current condition, previous hammer prices, and demand trends.