To estimate a maximum purchase price for the coin in question, we can analyze the provided data, especially the previous auction prices and the current condition of the coin.

1. Current condition: The coin has a condition of 80 (VF+), which indicates that it is in quite good shape. This is important because coins in better condition tend to fetch higher prices at auctions.

2. Previous auction prices: By looking at the auction prices of coins with a similar condition (80), we can see that they have reached auction prices that vary, but many are in the range of 200 to 300 euros. For example:
- 280 euros (2020-12-16)
- 240 euros (2020-03-12)
- 300 euros (2019-11-13)
- 250 euros (2018-04-25)

3. Average auction price: The average auction price for this coin is 317.34 euros, which also suggests that the auction price can be considerably higher than the starting price.

4. Starting price: The starting price is 150 euros, which is relatively low compared to previous auction prices.

Based on this data, an estimated maximum purchase price could be in the range of 300 to 350 euros, considering that the condition is good and the average auction price is 317.34 euros. Therefore, a reasonable maximum purchase price could be:

Estimated maximum purchase price: 350 euros.