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

1. Starting price: 1500 euros.
2. Coin condition: 80 (MBC+), which is a fairly good condition.
3. Auction history:
- The average hammer price in previous auctions is 1365.75 euros.
- In recent auctions, the hammer price has been around 1500 euros or more, especially for coins with similar conditions.
- In previous auctions, hammer prices have reached up to 1700 euros for coins with conditions of 80 and 90.

4. Price trends:
- In the most recent auctions, hammer prices have shown an upward trend, reaching up to 1766 euros in a recent auction with a condition of 85.

Given that the coin has a condition of 80 and considering the hammer price history, an estimated maximum purchase price could be in the range of 1600 to 1800 euros. This is based on the fact that the starting price is 1500 euros and that higher prices have been reached in recent auctions for similar conditions.

Therefore, an estimated maximum purchase price could be approximately 1700 euros.