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

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

2. Starting Price and Previous Prices: The current starting price is 700 euros, and the average hammer price in previous auctions is 707.62 euros. This suggests that the starting price is reasonable and that there is a good chance it will sell for a similar or higher price.

3. Sales History: The coin has been auctioned 45 times, of which 42 have resulted in sales. This indicates a consistent interest in the coin, which can positively influence its price.

4. Previous Hammer Prices: Looking at previous hammer prices, there are examples of sales that have reached significantly higher prices, especially in similar conditions. For instance, in 2011, a coin with a condition of 90 sold for 1200 euros.

5. Recent Trends: In recent auctions, hammer prices have varied, but there are examples of similar coins that have sold for prices exceeding 1000 euros.

Based on these factors, an estimated maximum purchase price for this coin could be between 1000 and 1200 euros, considering its good condition and the demonstrated interest in previous auctions. However, since the starting price is 700 euros, it is likely that buyers will be willing to bid beyond this price, especially if there is competition in the auction.