Where can I get reasonably priced bedroom furniture?

I recently moved into my own apartment and so I’m still pretty new to furniture shopping. A friend of mine let me borrow her bed since she lives with her boyfriend and they use his, but they’re moving to a new apartment and she’s asked for it back. I’m in need of a mattress/box spring, a bed frame, a nightstand, and (possibly) a dresser. I’m on a tight budget (I have about $300 to work with) so I’m not looking for top of the line stuff. Where would you suggest I go for the best prices? Also, is it essential to have both a bed frame and a box spring or can I make do with just one of the two?

Thank you!!

P.s. For reference, I live in the US.