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 good shape. This generally translates to a higher price compared to coins in lower condition.

2. Auction History:
- The average hammer price for similar coins has been 151.54 euros.
- In previous auctions, we have seen hammer prices that varied significantly, from 17 euros to 950 euros, depending on the condition and demand at that time.
- The last auction with a similar condition (90) had a hammer price of 150 euros.

3. Starting Price and Average Starting Price:
- The current starting price is 110 euros, which is a good starting point.
- The average starting price of 77.57 euros suggests that, in general, coins of this reference tend to start at lower prices, but this may not reflect the actual value of the coin in good condition.

4. Recent Trends: In the most recent auction, a coin with a condition of 100 sold for 950 euros, indicating that there is a strong market for high-quality coins.

Based on these factors, an estimated maximum purchase price for the coin in condition 90 could be between 200 and 300 euros, considering that the average hammer price is 151.54 euros and there is potential for an increase due to the good condition and market demand.

Therefore, a reasonable maximum purchase price could be 250 euros.