To estimate a maximum purchase price for the coin that will be auctioned, we can analyze the provided data, including the starting and final prices of previous auctions, as well as the condition of the coins.

1. Current starting price: 300 euros.
2. Average final price in the past: 380.91 euros.
3. Auction history: The coin has been auctioned 13 times, of which it has sold 12 times. This indicates good demand.
4. Condition: There is no information about the condition of the current coin, but in the past, coins with a condition of 100 have reached final prices of up to 700 euros.

### Analysis of previous prices:
- The auction with a condition of 85 had a final price of 250 euros.
- Auctions with a condition of 100 had final prices of 700 euros.
- The most recent auction with a condition of 95 had a final price of 340 euros.

### Estimation:
Since there is no information about the condition of the current coin, but considering that there have been previous auctions with high conditions that have reached significant final prices, we can make a conservative estimate.

- Average final price: 380.91 euros.
- Price trend: Final prices have varied, but in general, coins in good condition have reached higher prices.

### Estimated maximum purchase price:
Taking into account the starting price of 300 euros and the average final price of 380.91 euros, an estimated maximum purchase price could be around 400 euros, considering that there may be competition in the auction and that interest in the coin could lead to a higher final price.

Estimated maximum purchase price: 400 euros.