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

1. Current Condition: The coin has a condition rating of 80 (MBC+), which indicates that it is in relatively good shape, although not the best possible condition.

2. Auction History:
- The average hammer price in previous auctions is 90.88 euros.
- In past auctions, hammer prices have varied significantly, with some reaching up to 250 euros in similar conditions (condition of 95).
- The last auction with a condition of 80 had an estimated price of 20 euros, but the hammer price is not available.

3. Starting Price and Average Starting Price:
- The current starting price is 12 euros, which is quite low compared to the average starting price of 70.44 euros.

4. Sales Trends: Of the 32 times it has been auctioned, it has sold 19 times, indicating a reasonable sales rate.

Based on these factors, an estimated maximum purchase price could be in the range of 80 to 120 euros, considering that the condition is good and that the hammer price history suggests it could reach higher figures in auctions. However, since the starting price is low, it could be a good opportunity to acquire it at a more accessible price.

Therefore, a reasonable maximum purchase price could be 100 euros.