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 80 (MS+), indicating that it is in fairly good shape, but not the best possible condition.

2. Auction History:
- The average hammer price in previous auctions is 1075 euros, suggesting that, in general, coins of this reference tend to sell for above their starting price.
- The last auction with a known hammer price was 1700 euros, indicating a high potential for this coin, especially if it is in similar or better condition.

3. Starting Price and Estimates:
- The current starting price is 600 euros, which is slightly higher than the average starting price of 520 euros. However, the estimated price of 1200 euros for the upcoming auction suggests expectations for the coin to reach a higher price.

4. Sales Trends: The coin has been sold in 90.9% of the auctions it has participated in, indicating good demand.

Based on these factors, an estimated maximum purchase price could be around 1200-1400 euros, considering that the average hammer price is 1075 euros and that there are examples of sales above 1600 euros in the past. This also takes into account the current condition and interest in the coin.