There are really only two choices for "cheap as possible" with Canon lenses: an 18-55/3.5-5.6 kit lens, or a 50mm f/1.8 lens (used, Yongnuo, whatever). Which one you're going to want depends on how you plan to use the lens.
Lenses have two (sets of) numbers to describe them: the focal length and the maximum aperture.
The focal length describes the magnification/field of view of the lens. The smaller the number, the wider the view, the longer the number, the tighter the view and the "closer" you feel to the subject. What you see with your unaided eye is "normal", wider is "wide angle", and longer is "telephoto". The 18-55 is a wide to short-telephoto lens. It covers a decent useful range, and is a "walkaround lens" for shooting a variety of subjects such as landscapes, buildings, and people. The 50mm is normal on a film camera, but on a 350D will be slightly telephoto. It's probably best at shooting people. It's much less versatile for framing, as it's fixed at 50mm, while the 18-55 can go from 18mm to 55mm.
The max. aperture numbers, however, are quite different between the two lenses. f/3.5-5.6 is "slow"--that is, you'll probably need a decent amount of light to shoot with it handheld and still get shutter speeds that won't cause motion blur. Indoors without a flash is not where this lens is going to work well (although IS stabilization might help). A 50/1.8, otoh, has a much larger max. aperture (about 4-10 times bigger, depending on the focal length setting on the 18-55), and can let in 4-10x the light, letting you shoot with shutter speeds 4-10x faster. It also can create a thinner depth of field.
Which one you choose is up to you. But if "cheapest possible" is your only measure, then the Yongnuo 50mm f/1.8 is probably the winner at $50 new on B&H. But, for general usability, I'd recommend considering a Yongnuo 35/2 or a used 18-55 for around $100 instead. And if you care about getting a reliable lens, then a Canon 18-55 or 50/1.8 (preferably the newest STM versions) is going to be a much better bet than the YN cheapies.