To estimate a maximum purchase price for the coin in question, we can consider several factors based on the provided data:

1. Current Condition: The coin has a condition rating of 80 (MBC+). This is an important factor, as coins in better condition tend to reach higher prices.

2. Previous Auction Prices: By observing previous auction prices for coins with a similar condition (around 80), we can see that they have reached auction prices that vary, but some examples are:
- 54 (2020-10-20, condition 80)
- 76 (2020-07-08, condition 85)
- 121 (2021-06-22, condition 90)
- 110 (2023-03-22, condition 90)

3. Average Auction Price: The average auction price for this coin is 116.27 euros, indicating that, in general, coins of this reference tend to sell for over 100 euros.

4. Recent Trends: In the most recent auctions, the auction prices have shown a range that may indicate an increase in interest or value for the coin.

5. Starting Price: The starting price is 18 euros, which is quite low compared to previous auction prices.

Based on these factors, an estimated maximum purchase price for this coin, considering its condition and previous auction prices, could be in the range of 120 to 150 euros. This is based on the auction price trends for coins of similar condition and the general interest in the coin.