To estimate a maximum purchase price for the coin in question, let's consider several factors:

1. Starting Price: 3000 euros.
2. Condition: The coin has a condition of 80 (MS+), indicating that it is in quite good shape.
3. Historical Data:
- In December 2018, a coin with a condition of 75 was auctioned with a starting price of 4000 euros and sold for 6000 euros.
- In March 2018, another coin with the same condition of 75 had a starting price of 1500 euros and sold for 3800 euros.

4. Average Hammer Price: 4533.33 euros, indicating that, in general, coins of this reference tend to sell above their starting price.

Given that the condition of the coin in question is better (80) than the previous ones (75), it is reasonable to assume that its hammer price could be higher than the previous examples.

### Estimation of the Maximum Purchase Price:
- Considering the average hammer price (4533.33 euros) and the fact that the condition is better, we could estimate that the hammer price could be in a higher range.
- A conservative approach could be to add 10-20% to the average hammer price, given the state of preservation.

Therefore, an estimated maximum purchase price could be in the range of 5000 to 5500 euros. This is based on the trend of previous prices and the better condition of the current coin.