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 (MBC+), indicating that it is in relatively good shape, but not among the best qualities (FDC).

2. Auction History:
- The average hammer price for similar coins in the past is 187.44 euros.
- The condition of coins auctioned in the past varies, but those with a similar condition (around 80-90) have reached hammer prices ranging from 175 to 495 euros, depending on demand and other factors.

3. Starting Price and Estimates:
- The current starting price is 20 euros, which is quite low compared to the average hammer price.
- The average starting price for similar coins is 117.29 euros, suggesting there is potential for an increase in the hammer price.

4. Recent Trends:
- In recent auctions, coins with similar conditions have had hammer prices that vary, but overall, prices have been on the rise.

Based on these factors, an estimated maximum purchase price for this coin could be in the range of 200 to 250 euros. This is based on the historical hammer prices for coins of similar condition and the potential for an increase in the hammer price in the current auction.