What’s a good cheap (under 100 dollar) capture card that I can get?)

Well it completely depends on what you are capturing. Older stuff like Wii, PS2, gamecube etc can be captured with something like a GV2-USB which you can pick up for like $20 on amazon. Anything HD I would prob advise a used 1st gen Elgato Game Capture on ebay

(For a switch)

For Switch you will need HDMI capture. 1st Gen elgato will be your ticket.

I recently went through figuring out HDMI capture for the switch and ended up buying a refurbished Elgato HD60s for around 70$.

Take a read though this thread for other recommendations and my own observations with it: https://www.speedrun.com/streaming_recording_equipment/thread/havyr