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:
- In the past, coins with a grade of 80 (MBC+) have been auctioned, and their hammer prices have varied. Here are some examples:
- 2020-10-20: Hammer price €35 (starting price €25)
- 2020-02-12: Hammer price €25 (starting price €18)
- 2018-09-19: Hammer price €40 (starting price €25)
- 2018-05-30: Hammer price €60 (starting price €60)
- 2019-03-14: Hammer price €100 (starting price €90)

2. Price analysis:
- The average hammer price for coins with a grade of 80 (MBC+) seems to be in the range of €25 to €60, with some exceptional cases reaching up to €100.
- The overall average hammer price for this coin is €58.59, indicating that there is considerable interest in this coin.

3. Maximum price estimation:
- Given that the coin's grade is 80 (MBC+) and considering the average hammer price of similar coins, a reasonable maximum purchase price could be in the range of €60 to €80.
- However, since the starting price is €30 and the average hammer price is €58.59, a prudent maximum purchase price could be €70.

Therefore, the estimated maximum purchase price for this coin would be €70.