To estimate a maximum purchase price for the coin that will be auctioned, we can analyze the provided data. Here are some key points to consider:

1. Starting price: 100 euros.
2. Average hammer price: 98.9 euros.
3. Auction history: The coin has been auctioned 1,295 times, of which it has sold 998 times. This indicates a relatively high sell-through rate.
4. Previous prices: There is a range of hammer prices in the past, with some reaching significantly higher figures, especially in higher grades.

Since there is no information about the grade of the current coin, it is prudent to take a conservative approach. However, it can also be noted that in previous auctions, some coins of the same reference have reached much higher hammer prices.

### Analysis of previous prices:
- Hammer prices have been recorded ranging from 15 euros to over 600 euros in different grades.
- The general trend shows that coins in better condition tend to achieve higher prices.

### Estimation:
- Given the starting price of 100 euros and the average hammer price of 98.9 euros, a reasonable maximum purchase price could be slightly higher than the starting price, considering the possibility that the coin may have a higher value in the market.

### Estimated maximum purchase price:
150 euros.

This price allows for a margin for competition in the auction, considering that some buyers may be willing to pay more for the coin, especially if there is interest in it.