To estimate a maximum purchase price for the coin in question, we can analyze the provided data, especially the previous auction prices and the current condition of the coin.

1. Current Condition: The coin has a condition rating of 90 (EF), indicating that it is in quite good shape.

2. Previous Auction Prices:
- In previous auctions, we have seen hammer prices that vary significantly. For example:
- A coin with a condition of 90 was auctioned for 1900 (2011-06-30).
- Another coin with a condition of 90 was auctioned for 1400 (2015-03-09).
- There are also examples of coins with lower conditions that sold for less, but the price range for similar conditions is relevant.

3. Average Hammer Price: The average hammer price for this coin is 1137.51, which gives us an idea of what buyers are willing to pay on average.

4. Starting Price: The starting price is 750, which is reasonable given the auction price history.

5. Estimation: Given that the condition of the coin is good (90) and considering the previous auction prices, a maximum purchase price could be in the range of 1500 to 2000 euros. This is based on the fact that coins in similar conditions have reached hammer prices in that range.

Therefore, an estimated maximum purchase price for this coin could be approximately 1800 euros.