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

1. Current starting price: 800 euros.
2. Condition of the coin: 80 (MBC+), which is a good condition, but not excellent.
3. Average auction price in the past: 1021.87 euros.
4. Previous auction prices for coins with similar condition (80):
- 600 euros (2020-12-16)
- 1300 euros (2020-12-16)
- 1400 euros (2020-10-21)
- 903 euros (2021-03-18)
- 705 euros (2021-10-20)
- 800 euros (2021-10-20)
- 1150 euros (2022-03-17)
- 1200 euros (2022-03-17)
- 1100 euros (2022-04-28)
- 1300 euros (2022-10-19)
- 1300 euros (2023-03-16)
- 1000 euros (2024-12-11)

5. Auction price analysis: Auction prices for coins with a condition of 80 have varied, but there are several examples that exceed 1000 euros. The average auction price (1021.87 euros) also suggests that the coin could sell for a price higher than the starting price.

6. Estimation of the maximum purchase price: Given that the average auction price is approximately 1021.87 euros and considering that the condition is good (80), a reasonable maximum purchase price could be in the range of 1100 to 1300 euros, taking into account that some auctions have reached up to 1400 euros in the past.

Therefore, an estimated maximum purchase price for this coin could be 1300 euros.