To estimate a maximum purchase price for the coin that will be auctioned, we can consider several factors based on the provided data:

1. Starting price: 60 euros.
2. Average hammer price: 98.9 euros.
3. Historical hammer prices: There are several previous hammer prices that vary considerably, but some of the highest are:
- 190 euros (condition 80)
- 230 euros (condition 90)
- 220 euros (condition 90)
- 350 euros (condition 90)
- 400 euros (condition 90)
4. Condition of the coin: No information is provided about the condition of the coin in the current auction, which makes the estimation more complicated. However, the highest hammer prices correspond to coins in good condition (condition 80-90).

Given that the average hammer price is 98.9 euros and considering that in previous auctions hammer prices have reached up to 400 euros for coins in similar conditions, a reasonable maximum purchase price could be slightly higher than the average hammer price, but not as high as the extreme prices.

Estimated maximum purchase price: 150 euros.

This price reflects a balance between the starting price, the average hammer price, and historical prices, taking into account the uncertainty regarding the condition of the coin.