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), indicating that it is in quite good shape. This generally translates to a higher price compared to coins in lower conditions.

2. Starting Price and Previous Prices: The current starting price is 4000 euros. In previous auctions, the average hammer price has been approximately 2934.31 euros, suggesting that the starting price may be a bit optimistic, but not unusual for a coin in good condition.

3. Price Trends: By observing previous hammer prices for coins with similar conditions (around 85-95), we can see that hammer prices have varied, but generally, coins in EF condition tend to reach higher prices. For example, in recent auctions, coins with a condition of 85 have reached hammer prices of up to 3600 euros.

4. Supply and Demand: The coin has been auctioned 42 times, with a sell-through rate of 81% (34 out of 42). This indicates good demand, which can push the price upwards.

5. Comparison with Previous Prices: In previous auctions, coins with similar conditions have reached hammer prices ranging from 2200 to 8000 euros, depending on the condition and demand at that time.

Taking all these factors into account, an estimated maximum purchase price for this coin could be around 5000 euros. This price reflects a balance between the current condition, market price trends, and the demand observed in previous auctions.