To estimate a maximum purchase price for the coin in question, we can analyze the provided data:

1. Current starting price: 90 euros.
2. Coin condition: 90 (EBC), indicating good condition.
3. Auction history:
- It has been auctioned 16 times, of which it has sold 13 times.
- The average hammer price in the past is 149.32 euros.
- In previous auctions, the hammer price has varied, with a maximum of 406.86 euros in 2016 for a coin with a condition of 90.

4. Recent hammer prices:
- In October 2022, a coin with a condition of 90 was auctioned and sold for 340 euros.
- In other auctions, hammer prices have ranged between 65 and 406.86 euros, depending on condition and demand.

Given that the coin to be auctioned has a condition of 90 and considering the hammer price history, an estimated maximum purchase price could be set in a range between the average hammer price (149.32 euros) and the highest recorded price (406.86 euros).

However, since the starting price is 90 euros and considering that the average hammer price is significantly higher, a reasonable maximum price could be:

Estimated maximum purchase price: 300 euros.

This price reflects a balance between the hammer price history and the current condition of the coin.