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

1. Condition: The coin to be auctioned has a condition of 80 (MBC+). This is lower than the coins that have been sold in the past, which have a condition of 90. Generally, better condition translates to a higher price.

2. Previous auction prices: Previous auction prices for coins with a condition of 90 have been 600, 310, and 300 euros. This suggests that, under similar conditions, the auction price could be quite high.

3. Average auction price: The average auction price for this coin has been 403.33 euros, providing an additional reference.

4. Starting price: The starting price is 80 euros, indicating that the auction house expects moderate interest in the coin.

Given that the condition of the coin being auctioned is lower than those that have been sold previously, and considering the average auction price, an estimated maximum purchase price could be set at a lower range than the previous auction prices, but still, it could be attractive to a collector.

Taking all these factors into account, an estimated maximum purchase price could be around 250-300 euros. This is based on the current condition and historical interest in the coin, as well as the average auction price.