To estimate a maximum purchase price for the coin in question, we can analyze the provided data:

1. Starting price: 300 euros.
2. Current condition: 70 (VG-).
3. Auction history: It has been auctioned 8 times and sold on all occasions.
4. Average hammer price: 414.13 euros.
5. Previous hammer prices:
- 500 euros (condition 85)
- 480 euros (condition not specified)
- 340 euros (condition not specified)
- 316 euros (condition not specified)
- 372 euros (condition not specified)
- 445 euros (condition not specified)
- 400 euros (condition 70)
- 460 euros (condition 85)

Given that the current condition of the coin is 70, which is lower than the conditions of 85 that have reached higher prices (500 and 460 euros), it is reasonable to assume that the hammer price will not reach those levels.

However, the average hammer price of 414.13 euros and the hammer price of 400 euros in a recent auction with the same condition suggest that the price could be in a similar range.

Taking all these factors into account, an estimated maximum purchase price could be around 400-450 euros, considering that condition is an important factor and that the average hammer price is 414.13 euros.

Therefore, a reasonable maximum purchase price could be 450 euros.