How long is a piece of string?
Depending on your interests and thus the type of electronics you are working with you could need anything from 40 AWG magnet wire to silicone covered 4 AWG (fine stranded, extra flexible) if you are working with high current DC motors. What you use for hook-up wire depends on the voltages an currents you are working with. Also, that's leaving out the whole world of multi-conductor cables.
Buy what you actually need when you need it, and if its less than $0.25 per foot, and you are certain you'll need more of the same within a year, buy a small reel rather than cut cable. You wont find much decent wire in the hardware store - you'll probably have to buy online.
I scrounge as much as possible - if the cable jacket or single wire insulation is intact and can wipe clean, it gets coiled and tagged and goes in the 'good' bins rough sorted by type, but if the jacket's crappy, I'll strip multi-conductor cable for hookup wire. I throw back crappy coax, thin screened cable and single wire as it isn't worth dealing with crap. Shorter offcuts of high core count multicore can be useful, otherwise its not worth bothering with anything much under 5 foot.
N.B. learning to distinguish real copper wire from CCA and CCS is an essential scrounger's life skill. Carry wire cutter/strippers, a small magnet and a lighter (for CCA flame test) and use them as CCA and CCS cable aren't even worth pulling out of a skip.