Trekking poles are like any other piece of outdoor gear: you need to base it on use, and not be afraid to spend $$ on quality.
You are highly unlikely to find a mountain hunter or someone packing a moose quarter using cheap poles. If you've ever seen someone under load on a downhill when one collapses, you'll know why.
If you are not gaining big elevation, or under serious load, a walking stick that you find or cut down is probably the ticket.
Leki, Black Diamond and Komperdell all make great poles. Stay away from "anti-shock" or "anti-vibration" styles. More weight, and noisy.