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

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

2. Auction history: By looking at the hammer prices of coins with similar conditions (around 90), we can see that the hammer prices have varied. For example:
- In previous auctions, coins with a condition of 90 have reached hammer prices of up to 230 euros (as in the auction on 2022-03-17).
- There are also examples of coins with a condition of 85 that have sold for around 120 euros.

3. Starting price and average hammer price: The current starting price is 100 euros, and the average hammer price in the past has been 84.28 euros. This suggests that the hammer price may be above the starting price, especially for a coin in good condition.

4. Recent trends: In the most recent auctions, hammer prices for coins of similar condition have shown an increase, which could indicate a rising trend in interest for these coins.

Based on these factors, an estimated maximum purchase price for this coin could be between 150 and 200 euros. This is based on the fact that, given its condition and the history of hammer prices, it is reasonable to expect that bidders would be willing to pay a price that reflects its quality and demand in the current market.

Therefore, an estimated maximum purchase price could be 200 euros.