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

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:
- The average auction price for coins with a similar condition (80) has been approximately 604.53 euros.
- In previous auctions, the hammer prices for coins with a condition of 80 have varied, with some examples being:
- 600 euros (2020-12-16)
- 460 euros (2020-02-13)
- 456 euros (2019-03-14)
- 505 euros (2017-07-05)
- 600 euros (2023-01-31)

3. Price Trends:
- The general trend shows that coins with a condition of 80 have had hammer prices ranging between 400 and 850 euros in the past, depending on demand and other market factors.

4. Starting Price: The starting price of 300 euros is reasonable and is below the average hammer price, suggesting that there could be room for the hammer price to be higher.

### Maximum Purchase Price Estimation
Given that the condition is good and considering the previous hammer prices, a reasonable maximum purchase price could be in the range of 600 to 800 euros. This is based on the average hammer price and the higher hammer prices observed in the past for coins with a similar condition.

Maximum Purchase Price Estimate: 800 euros.

This price reflects a balance between the condition of the coin and the previous hammer prices, taking into account that the market may fluctuate.