Place to get Cheap Bike?

Hey everyone,

I'm a college student that came down from NC to be with my family during this pandemic and have assumed a role of head of household while I'm here so that my grandmother doesn't work.

I just wanted to ask where would be the best place to buy a bike for one of my younger siblings that really needs an outlet during all this.

Having to work for the household has me a bit strained so I'd love to know where I can get a bike for cheap because I'd really want to get a bike as soon as I can to get my younger brother out of the house to not feel as cooped up.

For sizing, my sibling is in fourth grade about 4'0.

Any recommendation would be appreciated given that I don't know the area well. Thanks and have a blessed day reddit!