Can't be in Taiwanese dollars otherwise each drone would cost much less than the American unit price. The 600M USD must include other weapons. Even 4 MQ-9 for 600M is 150M each. Even accounting for A LOT of spares and A LOT of weaponry and dedicated 24 hour crews Reaper concierge service lol, that's still 100M USD more for each than what another customer would be paying.
This means either the 600M estimate is off, it's including plenty of other equipment and weapons, or some people in Taiwan are pocketing a nice bit of change. Probably a combination of all three.
The primary source is available in the article:
No armaments in the list
Yes, only 4 drones
Support, training, and related non-weapons systems included (and weapons hard points)
This recent batch of arms sales to Taiwan is reeking of corruption of at least one side if not both. None of these prices make sense. Even if Taiwan doesn't get to choose who to buy from (basically US only), I'm not sure why they would choose getting ripped off. If Turkey can make an effective armed drone, I don't see how Taiwan would not be able to.
4 unarmed drones will not provide any meaningful enhancements of existing capabilities, which you can at least say for 400 Harpoons, even if the Harpoons are overpriced.