How canI find out how many points I will get for making a giveaway for a certain game?

I think if it's been on sale for more than 90%, it acts as bundled. But yes, if you see a $10 game at 75% off for $2.50, it'll add $10 to your CV still.

If it has been in a bundle which means sold in a game bundle or discounted very deeply (as in a 95% discount or more I think it is) it will be counted as bundled from the date it was in the bundle. That means even if the create a giveaway page doesn't mark it as bundled (one star next to names of bundled games, two stars next to zero cv games) it will still be retroactively changed for everyone who created a giveaway after it was first sold so cheaply or in a bundle.

So basically if you get it for very little money but it costs way more on Steam, it'll probably give you bundled CV even if the system doesn't flag it immediately. If you are desperate for max CV either buy bundles based on the most games for the least money, which means you'll be giving away a lot of trash and will likely have more than usual problems with the winners... or buy good quality games that are never discounted which means yous pend a lot more money but get a lot more CV for it.