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

1. Current asking price: 900 euros.
2. Average past asking price: 1200 euros.
3. Average past auction price: 1950 euros.
4. Condition of this coin: 95 (S/C-), indicating good preservation.
5. Previous prices for this coin:
- In December 2021, an estimated price of 2000 euros was set, and it sold for 1500 euros.
- In June 2022, an estimated price of 3000 euros was set, and it sold for 2400 euros.

Given that the condition of the coin is high (95), and considering the previous auction prices, we can make an estimation.

- The average auction price in the past has been 1950 euros, suggesting that buyers are willing to pay close to this figure for coins in similar conditions.
- The last auction shows a sale price of 2400 euros, indicating that there is potential for an increase in the auction price for well-preserved coins.

Taking these factors into account, an estimated maximum purchase price could be positioned between the average auction price (1950 euros) and the highest auction price observed (2400 euros).

Therefore, a reasonable estimated maximum purchase price could be 2400 euros. This reflects both the good condition of the coin and the market interest in such pieces.