I agree with most of the above posts with just one small addendum: why not buy both?
The CB, as pictured, is way overpriced. The rusted chain itself along with the half-flat rear tire should set off a very loud alarm. No front fender, a grooved front brake rotor, missing rear components - all indicate the status of this bike: a 30 year old beater.
IF it runs, offer the current owner maybe $150 and be willing to "negotiate" another 25 or 50 to make him feel good about the deal. Then be prepared to spend at least another $600 or more on missing parts, cables, brake components, chain, tires, tubes, valve stems and whatever else you later discover. Then you'll have ... yep, a thirty year old motorcycle. You might also factor in the cost of a cell phone and roadside insurance depending on your risk tolerance.
Buy a used SV (or something similar) too. Around here you're looking at $3 k or so that will get you much newer technology and if you find a good one, it will be pretty much ready to ride.
$4,000 will get you two bikes. Treat them both with kindness and care and you'll be rewarded with two different rides for your efforts.
P.S. Under no circumstances should you extend this analogy to members of the fairer sex.