Cheat Engine

[WorldWreckerYT]

So, I'm trying to set the prices of upgrades in an idle game I'm playing to 0, but I've been having an issue with the numbers being rounded to the nearest 3 significant figures. I also don't know what type of values are being used when dealing with numbers that big. Any help is appreciated.

[ParkourPenguin]

It could be anything. A lot of games I see dynamically calculate price as needed from other values: e.g. `initial_price * base ^ num_purchased`. Searching for the value you see on-screen won't give you anything useful. The only value you can search for that impacts the price of the item is the number of items you've purchased.
And that's not to mention the "big float" types that store stuff well beyond the maximum normal value of a double. I've seen some javascript games use a mantissa and exponent as two separate values; others do more interesting things (see Knuth's up-arrow notation).
There's no guarantee the game is doing either of these.

If the game was made using Unity, activate mono features and dissect mono. Maybe you'll find some class that tells you how values are stored.
If it's javascript, use a browser to view the source. You might need to unpack the asar file if it's a standalone game (e.g. steam).