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

1. Current Condition: The coin has a condition rating of 90 (EF), indicating that it is in quite good shape. This generally translates to a higher price compared to coins with lower conditions.

2. Auction History:
- The average hammer price for this coin is 153.52 euros.
- In previous auctions, we have seen hammer prices that varied significantly, with some reaching up to 1000 euros in exceptional conditions (such as in 2018 with a condition of 95).
- Recent trends show that hammer prices have been in the range of 130 to 380 euros for similar conditions.

3. Starting Price: The current starting price is 150 euros, which is a good indicator of the seller's expectations.

4. Demand and Supply: The coin has been auctioned 44 times, with a sell-through rate of 88.6% (39 out of 44). This suggests that there is consistent interest in this coin.

5. Recent Hammer Prices: The most recent hammer prices for coins with similar conditions (85-90) have been in the range of 260 to 380 euros.

Based on these factors, an estimated maximum purchase price for this coin could be between 300 and 380 euros, considering that the condition is good and there is a history of hammer prices that supports this estimate.

Therefore, a reasonable maximum purchase price could be 350 euros.