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

1. Condition of the current coin: 80 (MBC+)
2. Previous auction prices:
- 2020-11-24: 750 (condition 90)
- 2020-10-21: 916 (condition 95)
- 2022-03-17: 1400 (condition 95)
- 2022-04-28: 360 (condition 70)
- 2022-06-01: 700 (condition 75)
- 2022-12-14: Not available (condition 80)
- 2023-02-16: 550 (condition 80)
- 2023-03-16: 750 (condition 90)

3. Price analysis:
- The auction prices for coins with similar condition (80) have been 550, and there is no data for the other case, but the highest auction price for a higher condition (90 and 95) has been up to 1400.
- The average auction price for all auctions is 734.5, indicating that, in general, coins of this reference tend to sell above their starting price.

4. Estimation:
- Given that the condition of the coin is 80, and considering that the auction prices for similar conditions have been 550 and 360, we can estimate that a maximum purchase price could be in the range of 600 to 750 euros, taking into account that the starting price is 350 euros.

Therefore, an estimated maximum purchase price for this coin could be 750 euros.