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

1. Current Condition: The coin has a condition rating of 80 (MBC+). This is an important factor, as coins in better condition tend to reach higher prices.

2. Auction History:
- The coin has been auctioned 7 times and has sold on all occasions, indicating good demand.
- The average hammer price in previous auctions is 268.33 euros, which gives us a solid reference.

3. Previous Auction Prices:
- In 2020, it was auctioned with a starting price of 250 euros and sold for 280 euros with a condition of 85.
- In 2019, the hammer price was 220 euros with a condition of 85.
- In 2021, with a condition of 80, it was estimated at 325 euros and sold for 280 euros.
- In 2022, with a condition of 75, it was estimated at 300 euros, but it did not sell.

4. Price Trends:
- Hammer prices have fluctuated, but generally, they have been in the range of 220 to 280 euros for similar conditions.
- The trend seems to be that as the condition improves, the hammer price also tends to increase.

5. Current Starting Price: The starting price is 250 euros, which is a reasonable starting point.

Based on these factors, an estimated maximum purchase price could be in the range of 280 to 320 euros, considering that the current condition is 80 and that the price history shows that coins in similar conditions have reached hammer prices in that range.

Therefore, an estimated maximum purchase price could be 300 euros. This allows for a margin to compete in the auction, taking into account demand and price history.