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

1. Current starting price: 1300 euros.
2. Coin condition: 80 (MBC+), indicating good condition, although not the best.
3. Auction history:
- The coin has been auctioned 5 times and has sold on all occasions.
- The average starting price in previous auctions has been 1000 euros, and the average hammer price has been 1200 euros.
- In the most recent auction (2023), the starting price was 1100 euros, with an estimated price of 1600 euros, but the hammer price is unknown.

4. Previous hammer prices:
- In 2018, the hammer price was 1100 euros.
- In 2015, the hammer price was 850 euros.
- In 2014, the hammer price was 950 euros.
- In 2022, the hammer price was 1900 euros (with a condition of 85).
- In 2023, the hammer price is unknown.

Given that the condition of the current coin is 80, which is similar to that of the 2023 auction, and considering that the hammer prices in previous auctions have ranged from 850 to 1900 euros, we can make an estimation.

The highest hammer price in the past was 1900 euros, but that was for a coin in better condition (85). Therefore, it is reasonable to assume that the hammer price for the current coin could be in a lower range.

Taking into account the starting price of 1300 euros and the history of hammer prices, an estimated maximum purchase price could be between 1300 and 1600 euros, with 1600 euros being a reasonable upper limit given the price history and the condition of the coin.

Maximum purchase estimate: 1600 euros.