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

1. Current Condition: The coin has a condition of 75 (MBC), indicating that it is in an acceptable state, but not among the best qualities. This may influence the price, as coins in better condition tend to fetch higher prices.

2. Auction History:
- It has been auctioned 5 times in the past, of which it has sold 3 times. This indicates that there is interest in the coin, but also that there is a 40% chance it has not sold.
- Previous starting and final prices are relevant. For example, in 2019, the coin started at 900 euros and sold for 950 euros, suggesting that the final price may be close to the starting price in recent auctions.

3. Average Starting and Final Prices:
- The average starting price is 840 euros and the average final price is 1016.67 euros. This indicates that, in general, coins of this reference tend to sell for above their starting price.

4. Price Trends:
- The current starting price is 600 euros, which is lower than the average starting price. This could attract more bidders, but it may also indicate that the seller is looking for a quick sale.

5. Comparison with Previous Prices:
- In the most recent auction, the coin sold for 1000 euros with a condition of 70, which is lower than the current condition of 75. This suggests that the price could be higher in this auction.

Taking all these factors into account, an estimated maximum purchase price could be around 950-1100 euros, considering that the condition is better than in the previous auction and that interest in the coin seems to be moderate. A price of 1000 euros could be a reasonable target, given the auction history and the current condition.