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), 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:
- The average hammer price for this coin has been 64.1 euros.
- In previous auctions, we have seen hammer prices that varied significantly, ranging from 13 euros to 220 euros, depending on the condition and the context of the auction.

3. Starting Price and Previous Prices:
- The current starting price is 30 euros, which is relatively low compared to the average hammer price.
- In recent auctions, the hammer price has been around 30-35 euros for similar conditions.

4. Sales Trends: The coin has been sold in 23 out of 29 auctions, indicating good demand.

Based on these factors, an estimated maximum purchase price could be in the range of 80 to 120 euros, considering that the condition is good and that the price history shows that coins in similar conditions have reached higher prices in the past.

Therefore, a reasonable estimated maximum purchase price could be 100 euros.