We don't like to focus too much on lower-specced phones here, but with Christmas approaching, Nokia's Asha 500, 502 and 503 might be suitable PAYG options for your younger friends and family members.
So what's the difference between the three? The 500 has a 2MP camera and will cost $69 in the US (UK pricing hasn't been confirmed yet), and will have single-SIM or dual-SIM options. The 502 will cost $89 and come with a 5MP dual-swap SIM, and the 503, the one we'd recommend if you had to go low-end, has a 3MP camera but crucially 3G data connectivity, and will come in single and dual-SIM options for $99.
You can read more on this trio here.