To estimate a maximum purchase price for the coin in question, we will consider several factors, including the current condition of the coin, previous auction prices, and the starting price.

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

2. Previous auction prices:
- In previous auctions, we have seen hammer prices that vary significantly. For example, in 2020, a coin with a condition of 90 was auctioned for 1300 euros, while another with a condition of 85 sold for 1100 euros.
- In the most recent auction, a coin with a condition of 90 was hammered at 2300 euros, suggesting that there is a strong market for coins in good condition.

3. Average hammer price: The average hammer price for this coin is 1149.38 euros, which provides a useful benchmark.

4. Starting price: The starting price is 700 euros, which is reasonable given the history of hammer prices.

Taking all these factors into account, an estimated maximum purchase price could be in the range of 1500 to 2300 euros, considering that the condition is good and there is a history of hammer prices that supports this estimate.

Therefore, a reasonable maximum purchase price could be 2000 euros. This allows for some margin for competition in the auction, given the potential interest from other buyers.