To estimate a maximum purchase price for the coin with a grade of 80 (MBC+), we can analyze the historical data from previous auctions of coins with a similar grade and their hammer prices.

1. Relevant data from previous auctions:
- Coins with a grade of 80 (MBC+):
- Hammer price: 50 (2019-05-23)
- Hammer price: 30 (2019-09-19)
- Hammer price: 67 (2018-10-16)
- Hammer price: 41 (2018-12-11)
- Hammer price: 40 (2023-04-19)
- Hammer price: 110 (2021-06-22)
- Hammer price: 140 (2023-03-16)

2. Price analysis:
- The hammer prices for coins with a grade of 80 have varied, ranging from 30 to 140 euros.
- The average hammer price for coins with a grade of 80 seems to be in the range of 40 to 110 euros, with some higher peaks.

3. Additional considerations:
- The current starting price is 40 euros, and the average hammer price in the past has been 98.74 euros.
- Given that the coin's grade is 80, which is quite good, and considering the interest in the auction, a hammer price in the upper range could be reasonable.

4. Estimation of the maximum purchase price:
- Based on the previous analysis, a reasonable maximum purchase price could be in the range of 100 to 120 euros, considering that the average hammer price has been 98.74 euros and that there is potential for the price to rise in a competitive auction.

Therefore, an estimated maximum purchase price for this coin could be approximately 120 euros.