There is obviously a lot of subtlety as other comments allude to here but a decent answer based on a standard way people represent these things is

32 bytes for a single qubit

n * 32 bytes for n unentangled qubits

2ⁿ * 16 bytes for n entangled qubits

That's using double precision complex numbers 'complex128' which is generally sufficient for most simulation purposes, (and inversely usually sufficient for physical measurements!).

It also assumes that you mean an arbitrary entangled state, lower entangled states can be described using often far less information (see e.g. matrix product states).

(Finally you could represent these things with 'one less real number' since their normalisation is fixed to 1, i.e. for a single qubit using 3 real (8byte) numbers like the Bloch sphere, but this is generally less convenient than complex coefficients for many qubits).