I have a small 65mm quadcopter which uses 2s batteries. Is there a recommended LiPo C-rating to get for a drone like this? Or is there some way to figure out what C-rating I should get?
C rating is very much a non-science. There’s no real way to compare between brands, so just go off the idea that the higher the C value, the better.
If you want to do it a little more mathematically (though it still won’t be completely accurate), find out the maximum current draw of each of your motors and other electronics, add them up and then add a bit (maybe 20%) for some extra safety, and this will be your maximum current draw.
Divide this by the capacity of your battery in amp-hours (so 0.45 for a 450mAh battery) and this will give you your ideal C rating.
C ratings vary between brands, so it's hard to use it to compare batteries. While it defines the current the battery can provide, there's no standard for whether it means you can regularly fly at this level, use it for a 'short' burst (whatever that means) or whether the battery can manage that current briefly but will over-heat and never do it again.
If you fly with others who fly similar quads, you can see what brands they have tried and which they prefer. There are lots of blogs and videos that review a number of brands, although many are a paid adverts. Otherwise all you can do is buy a number of different brands and see which you like.