To estimate a maximum purchase price for the coin in question, we can 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 in the past is 188.08 euros.
- The highest hammer prices in previous auctions for coins with similar conditions (around 80-90) have been up to 490 euros (in 2017) and 320 euros (in 2020).

3. Starting Price and Average Starting Price:
- The current starting price is 150 euros, which is lower than the historical average hammer price. This suggests that there may be room for the hammer price to be higher.

4. Recent Trends: In the most recent auctions, hammer prices have varied, but overall, they have been in a range that suggests demand for this coin remains strong.

Based on these factors, an estimated maximum purchase price could be in the range of 250 to 300 euros, considering that the condition is good and that the price history shows similar coins have reached higher prices in the past.

Therefore, a reasonable maximum purchase price could be 300 euros.