To estimate a maximum purchase price for the coin in question, we will consider several factors:

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

2. Auction History:
- It has been auctioned 6 times in the past, of which 5 have sold. This indicates a consistent interest in the coin.
- The average starting price in previous auctions is 248.37 euros, and the average hammer price is 492.18 euros. This suggests that, in general, buyers are willing to pay a considerably higher price than the starting price.

3. Previous Prices:
- In the 2018 auction, the coin sold for 380 euros with a condition of 90.
- In 2020, it sold for 460 euros, also with a condition of 90.
- The 2015 auction had a hammer price of 1155.92 euros, but this seems to be an exceptional case, as the starting price was very high.

4. Condition Comparison: A condition of 80 is lower than the conditions of 90 in previous auctions that achieved hammer prices of 380 and 460 euros. This suggests that the hammer price for this coin could be lower than those values.

5. Estimation: Given that the average hammer price is 492.18 euros and considering that the current condition is lower than the conditions that achieved higher prices, an estimated maximum purchase price could be in a lower range.

Taking all these factors into account, an estimated maximum purchase price for this coin could be around 350 to 400 euros. This reflects a balance between the historical interest in the coin and its current condition.