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

1. Current Condition: The coin has a condition of 80 (MBC+), indicating that it is in fairly good shape, but not the best possible condition.

2. Previous Auction Prices:
- Auction prices for coins with similar conditions (around 75-85) have varied, but there are examples of auctions reaching up to 450 euros (such as in the auction on 2020-10-21).
- The average auction price for all auctions is 418.94 euros, suggesting that, in general, coins of this reference tend to sell for relatively high prices.

3. Auction Trends:
- The coin has been auctioned 21 times, of which 18 have sold. This indicates a consistent interest in the coin.
- The average starting price is 222.78 euros, which is also an indicator of demand.

4. Comparison with Starting and Auction Prices:
- The coin has a starting price of 200 euros, which is lower than the average starting price and the average auction price. This could indicate that there is potential for the auction price to be higher.

5. Estimation:
- Given that the condition is good and considering previous auction prices, an estimated maximum purchase price could be in the range of 400 to 500 euros, based on the historical behavior of coins with similar conditions.

Therefore, an estimated maximum purchase price for this coin could be approximately 450 euros.