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+). This is an important factor, as coins in better condition tend to reach higher prices.

2. Auction History:
- The average hammer price for similar coins has been 120.1 euros.
- In previous auctions, coins with a similar condition (80) have had hammer prices that varied, but there are examples of sales in the range of 100 to 110 euros.

3. Starting Price and Average Starting Price:
- The current starting price is 90 euros, which is lower than the average starting price of 111.47 euros. This suggests that there may be room for the hammer price to be higher.

4. Sales Trends:
- Out of the 36 times it has been auctioned, 30 have been sold, indicating good demand for this coin.

5. Previous Prices:
- In previous auctions, the hammer price for coins with a condition of 80 has been up to 100 euros, and in some cases, even higher.

Based on these factors, an estimated maximum purchase price could be in the range of 110 to 130 euros. This is based on the auction price history and the current condition of the coin. However, since the starting price is 90 euros, it is possible that the hammer price may not reach the estimated maximum, but it is reasonable to expect it to be within that range.