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

1. Current Condition: The coin has a condition rating of 30 (BC+), indicating that it is in a fairly deteriorated state. This will negatively affect its value compared to coins in better condition.

2. Auction History:
- In 2019, a similar coin was auctioned with a starting price of 1100 euros and a final price of 4500 euros, but it had a condition rating of 80, which is significantly better than the current condition.
- In 2017, another coin was auctioned with a starting price of 2000 euros and a final price of 3300 euros, but again, the condition is not specified, although it can be assumed to be better than the current one.
- In 2017, another auction had a starting price of 1100 euros and a final price of 1300 euros, indicating that the interest in that coin was lower.

3. Average Starting and Final Prices: The average starting price is 1150 euros and the average final price is 2400 euros. This suggests that, in general, coins of this reference tend to reach higher prices, but the condition of the current coin is a limiting factor.

4. Demand and Supply: Since the coin has been sold in all previous instances and there have been no failed sale attempts, this indicates that there is a consistent interest in this reference, although the current condition may limit the price.

Taking all these factors into account, an estimated maximum purchase price for this coin, considering its condition and auction history, could be in the range of 600 to 800 euros. This reflects a price that is reasonable given its state, but also takes into account the historical interest in the coin.